All About Coffee - William H. Ukers (best novel books to read .TXT) 📗
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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]:
Caffein exerts three important actions: (1) on the central nervous system: (2) on muscles, including cardiac: and (3) on the kidney. The action on the central nervous system is mainly on that part of the brain connected with psychical functions. It produces a condition of wakefulness and increased mental activity. The interpretation of sensory impressions is more perfect and correct, and thought becomes clearer and quicker. With larger doses of caffein the action extends from the psychical areas to the motor area and to the cord, and the patient becomes at first restless and noisy, and later may show convulsive movements.
Caffein facilitates the performance of all forms of physical work, and actually increases the total work which can be obtained from muscle. On the normal man, however, it is impossible to say how much of the action on the muscle is central and how much peripheral, but, as fatigue shows itself first by an action on the center, it is probable that the action of caffein in diminishing fatigue is mainly central. Caffein accelerates the pulse and slightly raises blood pressure. It has no action in any way resembling digitalis; by increasing the irritability of the cardiac muscle, its prolonged use rather tends to fatigue than to rest the heart.
Caffein and its allies form a very important group of diuretics. The urine is generally of a lower specific gravity than normal, since it contains a lesser proportion of salt and urea; but the total excretion of solids, both as regards urea, uric acid, and salts, is increased. Caffein, by exciting the medulla, produces an initial vaso-constriction of the kidneys, which tends at first to retard the flow of urine. So in recent years, other drugs have been introduced, allies of caffein, which act like it on the kidneys, but are without the stimulant action on the brain. Theobromine is such a drug.
Another authority states that[258]:
One of the most constant symptoms produced in man by over-doses of caffein is excessive diuresis, and experiments made upon the lower animals show that caffein acts as a diuretic not only by influencing the circulation, but also by directly affecting the secreting cells, the probabilities being in favor of the first of these theories of action. According to Schroeder, not only the water but also the solids of the urine are increased.
The question whether caffein has an influence upon tissue changes and the consequent nitrogenous elimination can not be considered as distinctly answered, though the most probable conclusion is that the action of caffein upon urea elimination and upon general nutrition is not direct or pronounced. While the therapeutic dose of caffein is broken up in the body with the formation of methylxanthin, which escapes with the urine, the toxic dose is at least in part eliminated by the kidney unchanged.
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
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