Stimulants.—Tea, coffee, and alcohol, are substances which, though taken with the food, are scarcely alimentary in any truer sense than some of the acrid seasonings just alluded to. Indeed, were the practice of chewing tobacco as prevalent as the use of these substances +, the leaf of this highly poisonous narcotic would be equally entitled to rank in the category of food. Still their habitual ingestion in company with other articles of diet, and the manner in which they modify nutrition, forbid them to be passed over unnoticed.
Tea and Ofee.— Tea and coffee present a marked similarity, not only in their com position, but also in that action on the ner vous system which is their chief physio logical effect on the organism. Both consist of an oil, with a certain quantity of tannin, united to an azotized vegetable alkaloid ; which is called thein, or caffein, respectively, but possesses the same composition in both (C4 o H,o N, 04). As regards their effects on the system, both produce sleeplessness and cere bral excitement. But coffee stimulates the circulation much more strongly, and in some persons excites diarrhcea. While tea is rnore apt to produce muscular tremors and irre gular cardiac action ; and generally causes a constipation rather than a relaxation of the bowels. The dietetic use of the two is very similar. Flow far they promote digestion is doubtful. They seem, however, to lessen the drowsiness and cerebral inaction which often follow the ingestion of a large meal. Like alcohol, they probably* diminish the rate of waste of the tissues generally.
Alcohol in all its various forms—whether of beer, wine, liqueur, or spirits—is equally un deserving of the name of food. It is not a nutritious article of diet ; but rather a drug, which ha.s a specific stimulating action on the nervous system. As regards its ultimate destiny in the organism, it seems certain that a part of it leaves the body, unchanged, in the exhalations of the skin and lungs.
The fermented liquors enumerated above are generally taken with the food. And in many of them, the alcohol is associated with small quantities of sugar and other alimentary substances. Their several tastes and odours are due partly to these, partly to other admixtures : — such as the bitter of the hop in beer, cenanthic wther in wine, and the various products of distillation in ardent spirits. The per centage of alcohol
in these different liquids may be estimated as being, on an average, 3 to 7 in beers ; 7 to 20 in wines ; and 20 to 60 in spirits.
Dietaries.— In ending this cursory view of the different alimentary substances, we may briefly inquire into the quantity and quality of the food which would be the result of their admixture with each other, in the proportions best suited to the maintenance of health.
From what has already been stated, it is obvious that, in constructing such an ideal diet, or in estimating the proper daily ration which ought to form the food of any indivi dual or class a persons, it should be our first care to ascertain the presence of all the ali mentary principles in suitable proportions.
At first sight, it might seem easy to cal culate an efficient scale of diet, from no other data but those which the above law affords us. With these data, it might even appear that such a knowledge of arith metic as is implied in knowing the rules of simple addition and subtraction would enable us to calculate an infinite number of dietaries. For, it would evidently- be easy for us to take any forms of protein, hydrocarbon, or hy drate of carbon, and compare the known per-centage of their elementary substances with the similar elements of the carbonic acid and urea which represent the most important products of the waste of the body. Adapting the quantities of the former to those of the latter, we might thus arrange thousands of for mulw,in which food would always cover waste, and income exceed expenditure: — formulm which, provided the human organism were really made up of similar figures, would, no doubt, give us equally definite and satisfactory results when carried out into practice.
A variety of circumstances,however, concur to invalidate such calculations, and reduce them to their true value:— viz. the results of a mere process of addition and subtraction, that only distort and obscure the facts on which they are founded. Such circumstances prove, that the end of these sums in simple arithmetic is no better than the beginning :— that they do but repeat, in a less specific, and therefore less truthful form, the various state ments of the skilful chemist, on which they are all based ; and that, if carried any further, they can only mislead the physiologist.