This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The immediate effects of coffee on the stomach result, I presume, from its direct contact with the tissue. Those upon the nervous system are probably produced by some one or more of its ingredients being absorbed, unaltered or modified, into the circulation. I do not know that any positive proof has been adduced upon this point. Certainly caffein does not escape with the urine; and the odour of coffee is not sensible in the breath or perspiration. A few years since some interesting experiments were made, which were supposed to prove that coffee and tea diminish the rapidity of the physiological change of structure in nutrition. It has been found that certain miners, and other labourers, are enabled, by the use of coffee, to do as much work, without loss of flesh or strength, upon a much smaller amount of food, as when they drink water alone ; and the experiments of Drs. F. W. Bocker and Julius Lehmann seemed to show, that the quantity of urea and other results of the metamorphosis of the tissues, lost through the emunctories, is much diminished by the use of these beverages. (See Brit. and For. Med.-chirurg. Rev., Oct. 1854, Am. ed., p. 313.)* These are important results: but I would attach a different explanation to them. It is difficult to conceive how stimulant medicines, which are acknowledged to increase the activity of the functions, particularly those of digestion and of the nervous system generally, can diminish the amount of organic change which takes place in the exercise of the functions. It is much more probable that these substances act by enabling the digestive organs, and others concerned in the conversion of the food into blood, to effect this conversion more thoroughly, and thus, not only to enable the system to do with less food, as the little which is used is thoroughly appropriated, but to diminish also the amount of excretion; because the food being converted more thoroughly into blood, is less wasted by those imperfect attempts at assimilation which only effect the change partially, and cause the remainder of the food to be thrown off in the form of urea. A proof of the correctness of this view is afforded by experiments of Dr. Bocker, which show that not only is the urea thrown off by urine diminished, but the amount of feculent matter discharged from the bowels is remarkably diminished also (Ibid.) Now it is much easier to conceive how a more thorough consumption of the food shall produce this diminution of feculent discharge, than that the same thing shall be effected by a reduction in the activity of the metamorphosis of the tissues in the nutritive process. Besides, it is the nitrogenous articles of food only to which the remark applies; and these are the very articles which alone can furnish urea by their imperfect conversion into blood or solid tissue. I believe, therefore, that, should this important result be verified, it would be really ascribable to the stimulant influence of the medicines upon the processes of digestion and assimilation, by which the nitrogenous food is more thoroughly converted into blood and consumed in nutrition, and consequently less of it escapes from the bowels undigested, and less from the kidneys, in the form of urea, in consequence of imperfect assimilation.* It is stated by Dr. Lehmann that, in persons following an active occupation, the use of an ounce of roasted coffee in infusion daily, reduces the daily waste one-fourth, and consequently diminishes, in the same proportion, the quantity of nitrogenous food neces-sary to health. (Ed. Month. Journ. of Med., Jan. 1855, p. 9.) It is not at all improbable, that the highly nitrogenous caffein is itself decomthe discharge of this principle. (Med. Times and Gaz., April, 1864, p. 419.) At present, therefore, the question must be considered as undecided; but in no event ran coffee be considered as exercising, in its immediate operation, a depressing influence on the nutritive process. (Note to the third edition).
* These results have been confirmed by the experiments of Dr. Wm. A. Hammond, of the U. S. Army, who. however, found all the constituents of the urine, and the quantity of the urine itself, to be diminished under the use of coffee and tea, which may, therefore, merely have acted as astringents, causing a retention of the urinary matters somewhat longer in the blood than in the state of health, without any reference to the disintegration of the tissues. (Am. Journ. of Med. Sci., N S., xxxi. p. 833.) - Note to the second edition.
Experiments by Mr. Charles E. Squarey, a report of which was presented by Dr. Garrod to the Royal Medical and Chirurgical Society of London, render doubtful the statements above made, in relation to the effect of coffee in diminishing the excretion of urea. Mr. Squarey's conclusion from his observations, which were made on the human subject, was that coffee neither increases, nor, to an appreciable extent, diminishes the proportion of urea eliminated by the kidneys (Med. T. and Gaz., Dec. 2, 1865, p. 613.) The researches of C. Voil, previously made, upon the effects of coffee on dogs, are of a similar bearing as to the diminution of the urea, which he found rather to be increased than otherwise. (Am. J. of Med. Sci., Oct. 1862, p. 507.) Still stronger is the statement of Dr. Geo. Harley, who asserts, as the result of his own observation, that coffee directly increases the excretion of urea; and ascribes the contrary results of Bocker and Hammond to their probably having drank their coffee with sugar, which is well known to have the effect of lessening posed, and made to contribute to the nourishment of the body; so that in this way also the necessary proportion of food is diminished.
* Confirmatory of these views are the results of experiments by Dr. John C. Draper, which prove that muscular exercise does not materially increase the amount of urea in the urine; while an increase of food has this effect. [X. Y. Journ. of Med., N. S., xvi. 167).
In relation to the different actions of the several constituents of roasted coffee, Dr. Lehmann thinks he has proved that the empyreumatic oil is that which most powerfully contributes to the results just stated, while it operates as a laxative, diaphoretic, and diuretic, invigorates the intellect, and, in excessive doses, produces irregular mental action, restlessness, and insomnolency. Caffein he found, in excess, to occasion rigors, acute pulse, urinary disorder, headache, and delirium. (Ibid., p. 314.) Experiments with caffein upon the lower animals seem to prove that it is poisonous in large doses. (Banking's Abstract, No. 29, p. 286).
The vapours from roasted coffee appear to have a powerful deodorizing effect, not merely by covering the offensive smell, but by decomposing the effluvia in which it originates. (See Am. Journ. of Pharm., xxviii. 183.) They appear also, when largely inhaled, to be capable of producing very serious effects on the nervous system. The cases of two soldiers are recorded by Dr. L. Traver, U. S. N., who, in consequence of smoking coffee as a substitute for tobacco, for a period of about ten days, were seized with a species of insanity. They either wandered about seemingly unconscious of what was going on around them, or sat as if in ruminating silence, starting with surprise when spoken to, staring at the speaker with a vacant and dejected look, and trembling with apparent apprehension of some evil to come. In consequence of their removal from the regiment, Dr. Traver lost sight of them, and was ignorant of the result. (Med. and Surg. Reporter, April 1, 1865, p. 406).
Tea differs in its effects from coffee mainly in degree. It is less stimulant to the nervous system, less apt to oppress the stomach, probably quite as efficient as a tonic to the digestive organs, and more astringent in consequence of the amount of tannic acid it contains. Certain it is that tea, especially black tea, may be drank habitually with impunity by persons who cannot use coffee without suffering, and that it sits more lightly on the stomach. In febrile diseases, a cup of tea is often not only tolerated, but agreeable to the patient, and refreshing in its effects; while coffee, however much it may be relished in health, is usually repulsive to the patient in a fever, and not well accepted by the stomach or the system.