By Charles W. Trigg

Industrial Fellow of the Mellon Institute of Industrial Research, Pittsburgh, 1916–1920

The published information regarding the effects of coffee drinking on the human system is so contradictory in its nature that it is hazardous to make many generalizations about the physiological behavior of coffee. Most of the investigations that have been conducted to date have been characterized by incompleteness and a failure to be sufficiently comprehensive to eliminate the element of individual idiosyncrasy from the results obtained. Accordingly, it is possible to select statements from literature to the effect either that coffee is an "elixir of life," or even a poison.

This is a deplorable state of affairs, not calculated to promote the dissemination of accurate knowledge among the consuming public, but it may be partly excused upon the grounds that experimental apparatus has not always been at the level of perfection that it now occupies. Also, to do justice to some of the able men who have interested themselves in this problem, it should be said that some of their results were obtained in researches, distinguished by painstaking accuracy, which have effected the establishment of the major reactions of ingested coffee.

The Physiological Action of Coffee

Drinking of coffee by mankind may be attributed to three causes: the demand for, and the pleasing effects of, a hot drink (a very small percentage of the coffee consumed is taken cold), the pleasing reaction which its flavors excite on the gustatory nerve, and the stimulating effect which it has upon the body. The flavor is due largely to the volatile aromatic constituents, "caffeol," which, when isolated, have a general depressant action on the system; and the stimulation is caused by the caffein. The general and specific actions of these individual components, together with that of the hypothetical "caffetannic acid," are considered under separate headings.

Coffee may be considered a member of the general class of adjuvant, or auxiliary, foods to which other beverages and condiments of negligible inherent food value belong. Its position on the average menu may be attributed largely to its palatability and comforting effects. However, the medicinal value of coffee in the dietary and per se must not be overlooked.

The ingestion of coffee infusion is always followed by evidences of stimulation. It acts upon the nervous system as a powerful cerebro-spinal stimulant, increasing mental activity and quickening the power of perception, thus making the thoughts more precise and clear, and intellectual work easier without any evident subsequent depression. The muscles are caused to contract more vigorously, increasing their working power without there being any secondary reaction leading to a diminished capacity for work. Its action upon the circulation is somewhat antagonistic; for while it tends to increase the rate of the heart by acting directly on the heart muscle, it tends to decrease it by stimulating the inhibitory center in the medulla.[188]

The effect on the kidneys is more marked, the diuretic effect being shown by an increase in water, soluble solids, and of uric acid directly attributable to the caffein content of the coffee taken. In the alimentary tract coffee seems to stimulate the oxyntic cells and slightly to increase the secretion of hydrochloric acid, as well as to favor intestinal peristalsis. It is difficult to accept reports of coffee accomplishing both a decrease in metabolism and an increase in body heat; but if the production of heat by the demethylation of caffein to form uric acid and a possible repression of perspiration by coffee be considered, the simultaneous occurrence of these two physiological reactions may be credited.

The disagreement of medical authorities over the physiological effects of coffee is quite pronounced. This may be observed by a careful perusal of the following statements made by these men. It will be noticed that the majority opinion is that coffee in moderation is not harmful. Just how much coffee a person may drink, and still remain within the limits of moderation and temperance, is dependent solely upon the individual constitution, and should be decided from personal experience rather than by accepting an arbitrary standard set by some one who professes to be an authority on the matter.

A writer in the British Homeopathic Review[189] says that "the exciting effects of coffee upon the nervous system exhibit themselves in all its departments as a temporary exaltation. The emotions are raised in pitch, the fancies are lively and vivid, benevolence is excited, the religious sense is stimulated, there is great loquacity.... The intellectual powers are stimulated, both memory and judgment are rendered more keen and unusual vivacity of verbal expression rules for a short time." He continues:

In apparent contradiction of this opinion, Dr. Valentin Nalpasse,[190] of the Faculty of Medicine of Paris, states:

Discussing the use and abuse of coffee, I.N. Love[191] says:

Also Dr. Jonathan Hutchinson[192] makes the following weighty pronouncement:

But Dr. Harvey Wiley[193] comes forth with evidence on the other side, saying:

Dr. V.C. Vaughn,[194] of the University of Michigan, speaking of tea and coffee, expresses this opinion:

This verdict is upheld by the results of a symposium[195] conducted by the Medical Times, in which a large majority of the medical experts participating, among whom may be enumerated Drs. Lockwood, Wood, Hollingworth, Robinson, and Barnes, agreed that the drinking of coffee is not harmful per se, but that over-indulgence is the real cause of any ill effects. This is also true of any ingested material.

Insomnia is a condition frequently attributed to coffee, but that the authorities disagree on this ground is shown by Wiley's[196] contention, "We know beyond doubt that the caffein (in coffee) makes a direct attack on the nerves and causes insomnia." While Woods Hutchinson[197] observes:

The writer has often had people remark to him that while black coffee sometimes kept them awake, coffee with cream or sugar or both made them drowsy.

In the course of experiments conducted by Montuori and Pollitzer[198] it was found that coffee prepared by hot infusion when given by mouth or hypodermically with the addition of a small dose of alcohol proved an efficient means of combating the pernicious effects of low temperatures. Coffee prepared by boiling, and tea, showed negative effects.

The value of coffee as a strength-conserver, and its function of increasing endurance, morale, and healthfulness, was demonstrated by the great stress which the military authorities, in the late and in previous wars, placed upon furnishing the soldiers with plenty of good coffee, particularly at times when they were under the greatest strain. Various articles[199] record this fact; and these statements are further borne out by the data given below in the discussion of the physiological effects of caffein, to which the majority of the stimulating effects of coffee may be attributed.

According to Fauvel,[200] with a healthy patient on a vegetable diet, chocolate and coffee increase the excretion of purins, diminishing the excretion of uric acid and apparently hindering the precipitation of uric acid in the organism. This diminution, however, was not due to retention of uric acid in the organism.

"Habit-forming" is one of the adjectives often used in describing coffee, but it is a fact that coffee is much less likely than alcoholic liquors to cause ill effects. A man rarely becomes a slave of coffee; and excessive drinking of this beverage never produces a state of moral irresponsibility or leads to the commission of crime. Dr. J.W. Mallet,[201] in testimony given before a Federal Court, stated that caffein and coffee were not habit-forming in the correct sense of the term. His definition of the expression is that the habit formed must be a detrimental and injurious one—one which becomes so firmly fixed upon a person forming it that it is thrown off with great difficulty and with considerable suffering, continuous exercise of the habit increasing the demand for the habit-forming drug. It is well known that the desire ceases in a very short period of time after cessation of use of caffein-containing beverages, so that in that sense, coffee is not habit-forming.

It has been shown by Gourewitsch[202] that the daily administration of coffee produces a certain degree of tolerance, and that the doses must be increased to obtain toxic results. Harkness[203] has been quoted as stating that "taken in moderation; coffee is one of the most wholesome beverages known. It assists digestion, exhilarates the spirits, and counteracts the tendency to sleep." Carl V. Voit,[204] the German physiological chemist, says this about coffee:

Dr. Brady[205] believes that the so-called harmfulness of coffee is mainly psychological, as evidenced by his expression, "Most of the prejudice which exists against coffee as a beverage is based upon nothing more than morbid fancy. People of dyspeptic or neurotic temperament are fond of assuming that coffee must be bad because it is so good, and accordingly, denying themselves the pleasure of drinking it."

The recounting of evidence, both pro and con, relevant to the general effects of coffee could continue almost ad infinitum, but the fairest unification of the various opinions is best quoted from Woods Hutchinson[206]:

So, if one is personally satisfied that he belongs to the abnormal minority, and has not been argued by fallacious reasoning into his belief that coffee injures him, he should either reduce his consumption of coffee or let it alone. Even those most vitally interested in the commercial side of coffee will admit that this is the logical procedure.

Effects of Coffee on Children

The same sort of controversy has raged around the question of the advisability of giving coffee to children as has occurred regarding its general action. Dr. J. Hutchinson[207] advocates furnishing children with coffee, while Dr. Charlotte Abbey[208] is strongly against such a practise, claiming that use of caffein-containing beverages before the attainment of full growth will weaken nerve power. Nalpasse[209] observes that until fully developed the young are immoderately excited by coffee; and Hawk[210] is of the opinion that to give such a stimulant to an active school-child is both logically and dietetically incorrect. Dr. Vaughn[211] advances this scientific argument against the drinking of coffee by children under seven years of age:

In a study of the effects of coffee drinking upon 464 school children, C.K. Taylor[212] found a slight difference in mental ability and behavior, unfavorable to coffee. About 29 percent of these children drank no coffee; 46 percent drank a cup a day; 12 percent, 2 cups; 8 percent, 3 cups; and the remainder, 4 or more cups a day. The measurements of height, weight, and hand strength also showed a slight advantage in favor of the non-coffee drinkers. If these results be taken as truly representative, their indication is obvious. However, it seems desirable to repeat these experiments upon other groups; at the same time noting carefully the factors of environment, and other diet, before any criterion is made.

As a refutation to this experimental evidence is the practical experience of the inhabitants of the Island of Groix, off the Brittany coast, whose annual consumption of coffee is nearly 30 pounds per capita, being ingested both as the roasted bean and as an infusion. It is reported that many of the children are nourished almost entirely on coffee soup up to ten years of age, yet the mentality and physique of the populace does not fall below that of others of the same stock and educational opportunities.[213]

Pertinent in this connection is Hawk's[214] statement that young mothers should refrain from the use of coffee, as caffein stimulates the action of the kidneys and tends to bring about a loss from the body of some of the salts necessary to the development of the unborn child as well as for the proper production of milk during the nursing period. The caffein of coffee also increases the flow of milk, but the milk produced is correspondingly dilute and a later decreased secretion may be expected. Furthermore, some of the caffein of the coffee may pass into the mother's milk, thus reaching the child, so that the use of coffee during the nursing period is undesirable on this ground also. Naturally, the question arises as to whether this arraignment is purely theoretical or based upon analytical and clinical data.

It is a difficult matter definitely to set an age below which coffee should not be drunk, as the time of reaching maturity varies with climate and ancestral origin. Yet, from a theoretical standpoint, children before or during the adolescent period should be limited to the use of a rather small amount of tea and coffee as beverages, as their poise and nerve control have not reached a stage of development sufficient to warrant the stimulation incident to the consumption of an appreciable quantity of caffein.

Coffee Drinking and Longevity

There are many who would have us believe that the use of coffee is only a means toward the end of quickly reaching the great beyond; but it is known that the habitual coffee drinker generally enjoys good health, and some of the longest-lived people have used it from their earliest youth without any apparent injury to their health. Nearly every one has an acquaintance who has lived to a ripe old age despite the use of coffee. Quoting Metchnikoff[215]:

The entire matter resolves itself into one of individual tolerance, resistivity, and constitution. Numerous examples of young abstainers who have died and coffee drinkers who have still lived on can be found, and vice versa, the preponderance of instances being in neither direction. Bodies of persons killed by accident have been painstakingly examined for physiological changes attributable to coffee; but no difference between those of coffee and of non-coffee drinkers (ascertained by careful investigation of their life history) could be discerned.[216] In the long run, it is safe to say that the effect of coffee drinking upon the prolongation or shortening of life is neutral.

Coffee in the Alimentary Tract

When coffee is taken per os it passes directly to the stomach, where its sole immediate action is to dilute the previous contents, just as other ingested liquids do. Eventually the caffein content is absorbed by the system, and from thence on a stimulation is apparent. Considerable conjecture has occurred over the difference in the effects of tea and coffee, the most feasible explanation advanced being one appearing in the London Lancet.[217]

This theory, if true, goes far toward explaining the more rapid stimulation of coffee.

The statement has sometimes been made that milk or cream causes the coffee liquid to become coagulated when it comes into contact with the acids of the stomach. This is true, but does not carry with it the inference that indigestibility accompanies this coagulation. Milk and cream, upon reaching the stomach, are coagulated by the gastric juice; but the casein product formed is not indigestible. These liquids, when added to coffee, are partially acted upon by the small acid content of the brew, so that the gastric juice action is not so pronounced, for the coagulation was started before ingestion, and the coagulable constituent, casein, is more dilute in the cup as consumed than it is in milk. Accordingly, the particles formed by it in the stomach will be relatively smaller and more quickly and easily digested than milk per se. It has been observed that coffee containing milk or cream is not as stimulating as black coffee. The writer believes that this is probably due to mechanical inclusion of caffein in the casein and fat particles, and also to some adsorption of the alkaloid by them. This would materially retard the absorption of the caffein by the body, spread the action over a longer period of time, and hence decrease the maximum stimulation attained.

In a few instances, a small fraction of one percent of coffee users, there is a certain type of distress, localized chiefly in the alimentary tract, caused by coffee, which can not be blamed upon the much-maligned caffein. The irritating elements may be generally classified as compounds formed upon the addition of cream or milk to the coffee liquor, volatile constituents, and products formed by hydrolysis of the fibrous part of the grounds. It may be generally postulated that the main causation of this discomfort is due to substances formed in the incorrect brewing of coffee, the effect of which is accentuated by the addition of cream or milk, when the condition of individual idiosyncrasy is present.

Without enlarging upon his reason, Lorand[218] concludes that neither tea nor coffee is advisable for weak stomachs. Nalpasse,[219] however, believes that coffee taken after meals makes the digestion more perfect and more rapid, augmenting the secretions, and that it agrees equally well with people inclined to embonpoint and heavy eaters whose digestion is slow and difficult. Thompson[220] also observes that coffee drunk in moderation is a mild stimulant to gastric digestion.

Eder[221] reported, as the result of an inquiry into the action of coffee on the activity of the stomachs of ruminants, that coffee infusions produced a transitory increase in the number and intensity of the movements of the paunch, but that the influence exercised was very irregular.

An elaborate investigation of the action of tea and coffee on digestion in the stomach was made by Fraser,[222] in which he found that both retard peptic digestion, the former to a greater degree than the latter. The digestion of white of egg, ham, salt beef, and roast beef was much less affected than that of lamb, fowl, or bread. Coffee seemed actually to aid the digestion of egg and ham. He attributed the retarding effect to the tannic acid of the tea and the volatile constituents of the coffee—the caffein itself favoring digestion rather than otherwise. Tea increased the production of gas in all but salt foods, whereas coffee did not. Coffee is, therefore, to be preferred in cases of flatulent dyspepsia.

Hutchinson, in his Food and Dietetics, opines:

Regarding increase in secretory activity, Moore and Allanston[223] report that in their experience meat extracts, tea, caffein solution, and coffee call forth a greater gastric secretion than does water, while with milk the flow of gastric juice seems to be retarded. Cushing[224] and others support this statement. This action is partially explained by Voit on the grounds that all tasty foods increase gastric secretion, the action being partly psychological; but Cushing observed the same effects upon introducing coffee directly into the stomachs of animals.

In general, a moderate amount of coffee stimulates appetite, improves digestion and relieves the sense of plenitude in the stomach. It increases intestinal peristalsis, acts as a mild laxative, and slightly stimulates secretion of bile. Excessive use, however, profoundly disturbs digestive function, and promotes constipation and hemorrhoids.[225] There is much evidence to support the view that "neither tea, coffee, nor chicory in dilute solutions has any deleterious action on the digestive ferments, although in strong solutions such an action may be manifest."[226] After conducting exhaustive experiments with various types of coffee, Lehmann[227] concluded that ordinary coffee is without effect on the digestion of the majority of sound persons, and may be used with impunity.

Coffee in the Dietary—Food Value

There are three things to be considered in deciding upon the inclusion of a substance in the dietary—palatability, digestibility without toxicity or disarrangement, and calorific value. Coffee is as satisfactory from these viewpoints as any other food product.

The palatability of a well-made cup of good coffee needs no eulogizing; it speaks for itself. It adds enormously to the attractiveness of the meal, and to our ability to eat with relish and appetite large amounts of solid foods, without a subsequent uncomfortable feeling. Wiley[228] says that the feeling of drowsiness after a full meal is a natural condition incidental to the proper conduct of digestion, and that to drive away this natural feeling with coffee must be an interference with the normal condition. However, if by so doing, we can increase our over-all efficiency without material harm to our digestive organs (and we can and do), the procedure has much in its favor both psychologically and dietetically.

The fact that coffee favors digestion without eventual disarrangement has been demonstrated above. On the subject of the relative agreement with the constitution of foods of daily consumption, Dr. English[229] said:

Further in this regard, Hutchinson[230] considers that ninety percent of the "dyspepsias" attributed to coffee are due to malnutrition, or to food simultaneously ingested, no disease known to the medical profession being directly attributable to it.

No one cognizant of the facts will contend that a cup of black coffee has any direct food value; but not so with the roasted bean. This has quite an appreciable content of protein and fat, both substances of high calorific value. The inhabitants of the Island of Groix eat the whole roasted coffee bean in considerable quantity, and seem to obtain considerable nourishment therefrom. Also, the Galla, a wandering tribe of Africa, make large use of food balls, about the size of billiard balls, consisting of pulverized coffee held in shape with fat. One ball is said to contain a day's ration; and, because of its food content and stimulating power, serves to sustain them on long marches of days' duration.

When an infusion, or decoction, of roasted coffee is made, about 1.25 percent of the extracted matter is protein, it being accompanied by traces of dextrin and sugar. The same dearth of extraction of food materials occurs upon infusing coffee substitutes. This small amount can have but little dietetic significance. However, upon addition of sugar and of milk or cream, with their content of protein, fat, and lactose, the calorific value of the cup of coffee rises. Lusk and Gephart[231] give the food value of an ordinary restaurant cup of coffee as 195.5 calories, and Locke[232] gives it as 156.

Mattei[233] found that 8 cc. of an infusion of roasted Mocha coffee of five-percent strength suppressed incipient polyneuritis in pigeons within a few hours' time. Their weight did not improve, but otherwise they were completely restored to health. However, in from four to six weeks after the apparent cure, the symptoms rapidly returned and the pigeons perished, with symptoms of paralysis and cerebral complications. The temporary cure was probably due to caffein stimulation and secondary actions of the volatile constituents of coffee, which may be related to the vitamines; for it is not likely that the vitamines would withstand the heat of roasting. If B-vitamine does occur in roasted coffee, it is present only in traces.[234]

The inclusion of coffee in the average dietary is warranted because of its evident worth as an aid to digestion and for its assimilating power, thus earning its characterization as an "adjuvant food."

Action of Coffee on Bacteria

The employment of coffee as an aid to sanitation has been but little considered. Coffee, when freshly roasted and ground, is deodorant, antiseptic, and germicidal, probably due to the empyreumatic products developed during the process of roasting. An infusion of 0.5 percent inhibits the growth of many pathogenic organisms, and those of 10 percent kill anthrax bacteria in three hours, cholera spirilla in four hours, and many other bacteria, including those producing typhoid, in two to six days.[235]

The maintenance of a low rate of contraction of typhoid fever has often been attributed to drinking of coffee instead of water, the action of the coffee being partly due to the bactericidal effect of the caffeol and partly to the boiling of the water before infusion. The stimulating tendency of the caffein to sustain and to "tide over" those of low vitalities is also evidenced.

Use of Coffee in Medicine

Coffee has been employed in medicinal practise as a direct specific, as a preventive, and as an antidote. The United States Dispensatory[236] summarizes the uses of caffein and coffee as follows:

Good effects of coffee are recounted by Thompson.[237]

Dr. Restrepo,[238] of Medellin, Colombia, claims to have cured many cases of chronic malaria and related diseases with infusion of green coffee, after quinine had failed. Wallace[239] states that tincture of green coffee is a natural and efficacious specific for cholera, and that she knows of more than a thousand eases of cholera and diarrhea which have been treated with it without an isolated case of failure. Landanabileo has been quoted as using raw coffee infusion in hepatic and nephritic diseases, venal and hepatic colics, and in diabetes.

In the Civil War, surgeons utilized coffee in allaying malarial fever and other maladies with which they had to contend, often under the most trying conditions, and with severely limited means of combating disease.[240] Its effect is to counteract the depressant action of low and miasmatic atmospheres, opening the secretions which they have checked. Travelers from the colder climes soon find that the fragrant cup of coffee is a corrective to derangements of the liver resulting from climatic conditions.[241]

Dr. Guillasse, of the French Navy, in a paper on typhoid fever, says:

Also it has been reported that in extreme cases of yellow fever, coffee has been used most effectively by many physicians as the main reliance after all other well known remedies have been administered and failed.

According to Lorand,[243] the use of coffee in gout is strictly prohibited by Umber and Schittenhelm; but he considered it a mistake absolutely to forbid coffee, as, when a person has good kidneys, the small amount of uric acid furnished by the caffein can readily be eliminated. A curious remedy for gout and rheumatism, the efficacy of which the writer scouts, is said to be[244]—a pint of hot, strong, black coffee, which must be perfectly pure, and seasoned with a teaspoonful of pure black pepper, thoroughly mixed before drinking, and the preparation taken just before going to bed. If this has any value, it is probably purely psychological in its function.

Several writers[245] attribute amblyopia and other affections of the sight to coffee and chicory, without giving much conclusive experimental data. Beer,[246] a Vienna oculist, however, held that the vapor from pure, hot, freshly-made coffee is beneficial to the eyes.

Coffee and caffein are physiologically antagonistic to the common narcotics, nicotine, morphine, opium, alcohol, etc., and are frequently used as antidotes for these poisons. Binz found that dogs that have been stupified with alcohol could be awakened with coffee. It may thus be prescribed for hard drinkers to counteract the baleful excitability produced by alcohol; in fact, many topers taper off after a long debauch with coffee containing small amounts of alcoholic beverages. Considering its ability to counteract the slow intoxication of tobacco, it may be inferred that coffee is indispensable for hard smokers.

In general, the medicinal value of coffee may be said to be directly attributable to its caffein content, although its antiseptic properties are dependent upon the volatile aromatic constituents. Its function is to raise and to sustain vitalities which have been lowered by disease or drugs. Although some of the cures attributed to it are probably purely traditional; still, it must be admitted, that by utilizing its stimulating qualities in many illnesses the patient may be carried past the danger point into convalescence.

Physiological Action of "Caffetannic Acid"

It has been demonstrated in chapter XVII that there is no definite compound "caffetannic acid," and that the heterogeneous material designated by this name does not possess the properties of tanning. Further substantiation of this contention, and more evidence of the innocuous character of the tannin-like compounds in coffee, are contained in the testimony of Sollmann.[247] "Tannins precipitate proteins, gelatine, and connective tissue, and thus act as astringents, styptics, and antiseptics. The different tannins are not equivalent in these respects. Some (which are perhaps misnamed) such as those of coffee and ipecac, are practically non-precipitant.... On the whole, one may say that the small quantities of tannin ordinarily taken with the food and drink are not injurious, but that large quantities (excessive tea drinking) are certainly deleterious. The tannin of coffee is scarcely astringent, and, therefore, lacks this action," which is proven by the fact that it does not precipitate proteins.

"It has been claimed that 'caffetannic acid' injures the stomach walls, but there is no evidence that this is so."[248] Wiley,[249] in reporting some of his experiments, says: "Apparently the efforts to saddle the injurious effects of coffee-drinking upon caffetannic acid in any form in which it may exist in the coffee-extract are not supported by these recent data." The fact that tannins retard intestinal peristalsis, whereas coffee promotes this digestive action, lends further proof to the non-existence of tannin in coffee. These statements by eminent authorities may be consolidated into the verity that there is no tannin, in the true sense of the term, in coffee; and that the constituents of the coffee brew which have been so designated are physiologically harmless.

Physiological Action of Caffeol

The evidence regarding the physiological action of caffeol is contradictory in many cases. J. Lehmann found in 1853, that the "empyreumatic oil of coffee, caffeone," is active; but more recent investigations have yielded results at variance with this. Hare and Marshall[250] believe that they proved it to be active. E.T. Reichert,[251] however, found it inactive in dogs, excepting in so far that, when given intravenously, it mechanically interfered with the circulation. With it Binz[252] was able to produce in man only feeble nervous excitement, with restlessness and increase in the rate and depth of respirations.

The general effects, as summated by Sollmann[253] are, for small doses, pleasant stimulation; increased respiration; increased heart rate, but fall of blood pressure; muscular restlessness; insomnia; perspiration; congestion; for large doses, increased peristalsis and defecation; depression of respiration and heart; fall of blood pressure and temperature; paralytic phenomena. It is doubtful whether the quantities taken in the beverage cause any direct central stimulation.

Investigations have also been conducted with the various known constituents of this "coffee oil." Erdmann[254] found that in doses of between 0.5 and 0.6 gram per kilo of body weight, furane-alcohol kills a rabbit by respiratory paralysis; and that the symptoms of poisoning are a short primary excitement, salivation, diarrhea, respiratory depression, continuous fall of the body temperature, and death from collapse with respiratory failure. In man, doses of from 0.6 to 1 gram of furane-alcohol increased respiratory activity without producing other symptoms.

However, man is not as susceptible to these compounds as are the smaller animals. But even if their relative susceptibility be assumed to be the same, the lethal dose given the rabbit is equivalent to giving a 140-pound man one dose containing the furane-alcohol content of over 5,000 cups of coffee. Thus, in view of the very apparent minuteness of the quantity of this compound present in one cup of coffee, together with the fact that it is not cumulative in its physiological action, the importance of its toxic properties becomes very inconsequential to even the most profuse and inveterate coffee drinkers.

Burmann[255] reported the volatile principle to have a reducing action on the hemoglobin; a depressing effect on the blood pressure; a depressant action on the central nervous system, disturbing the cardiac rhythm; and an action on the respiratory centers, causing dyspnea. The report of Sayre[256] regarding the minimum lethal dose of the concentrated combined active principles of coffee obtained from dry distillation is, for frogs, administered intraperitoneally and subcutaneously, 0.03 cubic centimeters per gram of body weight; for guinea pigs per stomach, 7.0 cc. per kilogram of body weight, and administered intravenously and intraperitoneally, about 1.0 cc. per kilogram.

This evidence regarding the physiological action of caffeol can not in any wise be construed to indicate a harmfulness of coffee. The percentage of these volatile substances in a cup of coffee infusion is so low as to be relatively negligible in its action. And, again, the caffein content of the brew, as will be seen, tends to counteract any possible desultory effects of the caffeol.

General Physiological Action of Caffein

More attention has been given to the study of the physiological action of caffein than to that of the other individual constituents of coffee. Since certain of the effects of coffee drinking have been attributed to this alkaloid, a brief presentment of the pharmacology of caffein will be given as an exposition of the many statements made regarding it. According to the British Pharmaceutical Codex[257]:

Another authority states that[258]:

The metabolism of the methyl purins, of which group caffein is a member, appears to vary with the quantity ingested. The manner in which the methyl group is liberated by the cell protoplasm is said[259] to determine the amount of stimulus which the tissues receive from these substances. The xanthin group is almost without any excitatory action, and its metabolic end products are constant. Perhaps the variation in the excretions of unchanged methylpurins is dependent upon the amount of total reactive energy they invoke.

Baldi[260] found that caffein in small doses increases muscular excitability in dogs and frogs. The spinal and muscular hyperic excitability produced by caffein is, in his opinion, due to the methyl groups attached to the xanthin nucleus. Fredericq[261] states that caffein increases the irritability of the cardiac vagus and accelerates the appearance of pseudofatigue of the vagus which is produced by prolonged stimulation of the nerve. The action of caffein on the mammalian heart has also been investigated by Pilcher,[262] who found that, following the rapid intravenous injection of caffein, there is an acute fall of blood pressure; and with a maximal quantity of caffein, 10 milligrams per kilogram, the cardiac volume and the amplitude of the excursions are usually unchanged. With larger quantities, the volume progressively increases and the amplitude of the excursion decreases.

Salant[263] found that the intravenous injection of 15 to 25 milligrams of caffein per kilogram in animals was followed by a fall of blood pressure amounting to 7 to 35 percent in most cases, which was transitory, although in some animals it remained unchanged. A moderate rise was rarely observed. Caffein aids the action of nitrates, acetanilid, ethyl alcohol and amyl alcohol, and increases the toxicity of barium chloride. In a very thorough study of the toxicity of caffein which he made with Reiger,[264] a greater toxicity of about 15 to 20 percent by subcutaneous injection than by mouth, and but about one-half this when injected peritoneally, was found. Intramuscularly the toxicity is 30 percent greater than subcutaneously. In making the tests on animals, they found that individuality, season, age, species, and certain pathological conditions caused variation in the toxic effect of the administered caffein. Low protein diet tends to decrease resistance to caffein in dogs, and a milk or meat diet does the same for growing dogs. Caffein is not cumulative for the rabbit or dog.

As a result of experiments on the action of caffein on the bronchiospasm caused by peptone (Witte), silk peptone, B-imidoazolyl-ethylamin, curare, vasodilation, and mucarin, Pal[265] concluded that caffein stimulates certain branches of the peripheral sympathetic and is thus enabled to widen the bronchi or remove bronchiospasm.

According to Lapicque[266], caffein produces a change in the excitability of the medulla of the frog similar to that produced by raising the temperature of the nerve centers. Schürhoff[267] has pointed out that the continued use of large quantities of caffein will produce cardiac irregularity and sleeplessness.

Cochrane[268] cited three cases where caffein was hypodermically administered in cases of acute indigestion, etc., and concluded that the cases prove that caffein, or a compound containing it as a synergist, does indirectly make the injection of morphia a safe proceeding, and directly increases the force of the heart and arterial tension. However, Wood[269] found that medium doses of caffein do not produce any marked rise in blood pressure, and cause a reduction in pulse rate. He attributes the contradictory results which prior investigations gave, to employment of unusually large doses and to inaccurate experimental methods.

Caffein was found by Nonnenbruch and Szyszka[270] to have a slight action toward accelerating the coagulation time of the blood, being active over several hours. It inhibits coagulation in vitrio. Its action in the body apparently rests on an increase of the fibrin ferment. There is no reason to believe that the behavior is dependent on a toxic action, but there is probably an action on the spleen; for in several rabbits from which the spleen was removed, no action was observed.

Experiments conducted by Levinthal[271] gave no positive information as to the formation of uric acid from caffein in the human organism. The elimination of caffein has also been studied by Salant and Reiger[272], who found that larger amounts of caffein are demethylated in carnivora than in herbivora, and resistance to caffein is inversely as demethylation, caffein being much more toxic in the former class. In a similar investigation, Zenetz[273] observed that caffein is very slightly eliminated from the system by the kidneys, and that its action on the heart is cumulative; therefore he concludes that it is contra-indicated in all renal diseases, in arterio-sclerosis, and in cardiac affections secondary to them. The inaccuracy of these conclusions regarding the non-elimination of caffein and those of Albanese,[274] Bondzynski and Gottlieb[275], Leven[276], Schurtzkwer[277], and Minkowski[278], has been shown by Mendel and Wardell[279], who point out that many of these experimenters worked with dogs, in which the chief end-product of purin metabolism is not uric acid, but allantoin. They observe that the increase in excretion of uric acid after the addition of caffein to the diet seems to be proportional to the quantity of caffein taken, and equivalent to from 10 to 15 percent of the ingested caffein. The remainder of the caffein is probably eliminated as mono-methylpurins.

Regarding the alleged cumulative action of caffein, Pletzer[280], Liebreich,[281] Szekacs[282], Pawinski,[283] and Seifert[284] all concluded from their investigations that the action of caffein is usually of brief duration, and does not have a cumulative effect, because of its rapid elimination; so that there is no danger of intoxication.

Dr. Oswald Schmiedeberg says:

According to Dr. Hollingworth's[285] deductions, caffein is the only known stimulant that quickens the functions of the human body without a subsequent period of depression. His explanation for this behavior is that "caffein acts as a lubricator for the nervous system, having an actual physical action whereby the nerves are enabled to do their work more easily. Other stimulants act on the nerves themselves, causing a waste of energy, and consequently, according to nature's law, a period of depression follows, and the whole process tends to injure the human machine." In not a single instance during his experiments at Columbia University did depression follow the use of caffein.

Of course, caffein, like any other alkaloid, if used to excess will prove harmful, due to the over-stimulation induced by it. However, taken in moderate quantities, as in coffee and tea by normal persons, the conclusions of Hirsch[286] may be taken as correct, namely: caffein is a mild stimulant, without direct effect on the muscles, the effect resulting from its own destruction and being temporary and transitory; it is not a depressant either initially or eventually; and is not habit-forming but a true stimulant, as distinguished from sedatives and habit-forming drugs.

Caffein and Mental and Motor Efficiency

The literature on the influence of caffein on fatigue has been summarized, and the older experiments clearly pointed out, by Rivers[287]. A summary of the most important researches which have had as their object the determination of the influence of caffein on mental and motor processes has been made by Hollingworth[288], from whose monograph much of the following material has been taken.

Increase in the force of muscular contractions was demonstrated in 1892 by De Sarlo and Barnardini[289] for caffein and by Kraepelin for tea. These investigators used the dynamometer as a measure of the force of contraction; however, most of the subsequent work on motor processes has been by the ergographic method. Ugolino Mosso[290], Koch[291]. Rossi[292], Sobieranski[293], Hoch and Kraepelin,[294] Destrée,[295] Benedicenti,[296] Schumberg,[297] Hellsten,[298] and Joteyko,[299] have all observed a stimulating effect of caffein on ergographic performance. Only one investigation of those reported by Rivers failed to find an appreciable effect, that of Oseretzkowsky and Kraepelin,[300] while Feré[301] affirms that the effect is only an acceleration of fatigue.

In spite of the general agreement as to the presence of stimulation there is some dissension regarding whether only the height of the contractions or their number or both are affected. As might be expected from the great diversity of methods employed, the quantitative results also have varied considerably. Carefully controlled experiments by Rivers and Webber[302] "confirm in general the conclusion reached by all previous workers that caffein stimulates the capacity for muscular work; and it is clear that this increase is not due to the various psychical factors of interest, sensory stimulation, and suggestion, which the experiments were especially designed to exclude. The greatest increase ... falls, however, far short of that described by some previous workers, such as Mosso; and it is probable that part of the effect described by these workers was due to the factors in question."

Investigations of mental processes under the influence of caffein have been much less frequent, most notable among which are those of Dietl and Vintschgau,[303] Dehio,[304] Kraepelin and Hoch,[305] Ach,[306] Langfeld,[307] and Rivers.[308] Kraepelin[309] observes: "We know that tea and coffee increase our mental efficiency in a definite way, and we use these as a means of overcoming mental fatigue ... In the morning these drinks remove the last traces of sleepiness and in the evening when we still have intellectual tasks to dispose of they aid in keeping us awake." Their use induces a greater briskness and clearness of thought, after which secondary fatigue is either entirely absent or is very slight.

Tendency toward habituation of the pyschic functions to caffein has been studied by Wedemeyer[310], who found that in the regular administration of it in the course of four to five weeks there is a measurable weakening of its action on psychic processes.

Rivers[311], who seems to have been the first to appreciate fully the genuine and practical importance of thoroughly controlling the psychological factors that are likely to play a rôle in such experiments, concludes that "caffein increases the capacity for both muscular and mental work, this stimulating action persisting for a considerable time after the substance has been taken without there being any evidence, with moderate doses, of reaction leading to diminished capacity for work, the substance thus really diminishing and not merely obscuring the effects of fatigue."

Subsequent to these investigations was that of Hollingworth[312] which is at once the most comprehensive, carefully conducted, and scientifically accurate one yet performed. He employed an ample number of subjects in his experimentation; and both his subjects, and the assistants who recorded the observations, were in no wise cognizant of the character or quantity of the dose of caffein administered, the other experimental conditions being similarly rigorous and extensive.

The purpose of his study was to determine both qualitatively and quantitatively the effect of caffein on a wide range of mental and motor processes, by studying the performance of a considerable number of individuals for a long period of time, under controlled conditions; to study the way in which this influence is modified by such factors as the age, sex, weight, idiosyncrasy, and previous caffein habits of the subjects, and the degree to which it depends on the amount of the dose and the time and conditions of its administration; and to investigate the influence of caffein on the general health, quality and amount of sleep, and food habits of the individual tested.

To obtain this information the chief tests employed were the steadiness, tapping, coordination, typewriting, color-naming, calculations, opposites, cancellation, and discrimination tests, the familiar size-weight illusion, quality and amount of sleep, and general health and feeling of well-being. A brief review of the results of these tests is given in the tabular summary.

From these Hollingworth concluded that caffein influenced all the tests in a given group in much the same way. The effect on motor processes comes quickly and is transient, while the effect on higher mental processes comes more slowly and is more persistent. Whether this result is due to quicker reaction on the part of motor-nerve centers, or whether it is due to a direct peripheral effect on the muscle tissue is uncertain, but the indications are that caffein has a direct action on the muscle tissue, and that this effect is fairly rapid in appearance. The two principal factors which seem to modify the degree of caffein influence are body weight and presence of food in the stomach at the time of ingestion of the caffein. In practically all of the tests the magnitude of the caffein influence varied inversely with the body weight, and was most marked when taken on an empty stomach or without food substance. This variance in action was also true for both the quality and amount of sleep, and seemed to be accentuated when taken on successive days; but it did not appear to depend on the age, sex, or previous caffein habits of the individual. Those who had given up the use of caffein-containing beverages during the experiment did not report any craving for the drinks as such, but several expressed a feeling of annoyance at not having some sort of a warm drink for breakfast.

It is interesting to note that he also found a complete absence of any trace of secondary depression or of any sort of secondary reaction consequent upon the stimulation which was so strikingly present in many of the tests. The production of an increased capacity for work was clearly demonstrated, the same being a genuine drug effect, and not merely the effect of excitement, interest, sensory stimulation, expectation, or suggestion. However, this study does not show whether this increased capacity comes from a new supply of energy introduced or rendered available by the drug action, or whether energy already available comes to be employed more effectively, or whether fatigue sensations are weakened and the individual's standard of performance thereby raised. But they do show that from a standpoint of mental and productive physical efficiency "the widespread consumption of caffeinic beverages, even under circumstances in which and by individuals for whom the use of other drugs is stringently prohibited or decried, is justified."

Conclusion

Brief summarization of the information available on the pharmacology of coffee indicates that it should be used in moderation, particularly by children, the permissible quantity varying with the individual and ascertainable only through personal observation. Used in moderation, it will prove a valuable stimulant increasing personal efficiency in mental and physical labor. Its action in the alimentary régime is that of an adjuvant food, aiding digestion, favoring increased flow of the digestive juices, promoting intestinal peristalsis, and not tanning any portion of the digestive organs. It reacts on the kidneys as a diuretic, and increases the excretion of uric acid, which, however, is not to be taken as evidence that it is harmful in gout. Coffee has been indicated as a specific for various diseases, its functions therein being the raising and sustaining of low vitalities. Its effect upon longevity is virtually nil. A small proportion of humans who are very nervous may find coffee undesirable; but sensible consumption of coffee by the average, normal, non-neurasthenic person will not prove harmful but beneficial.