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.