CHEMISTRY OF DIGESTION AND NUTRITION. 297 



mere pleasures of the palate, but their importance is of a subordinate character. 

 They may be omitted from the diet, as happens or may happen in the case of 

 animals, without affecting injuriously the nutrition of the body, although it is 

 probable that neither man nor the lower animals would voluntarily eat food 

 entirely devoid of flavor. 



Stimulants. The well-known stimulating effect of alcohol, tea, coffee, etc. 

 is probably due to a specific action on the nervous system whereby the irri- 

 tability of the tissue is increased. The physiological effect of tea, coffee, and 

 chocolate is due to the alkaloids caffein (trimethyl-xanthin) and theobromin 

 (dimethyl-xanthin). In small doses these substances are oxidized in the 

 body and yield a corresponding amount of energy, but their value from this 

 standpoint is altogether unimportant compared with their action as stimulants. 

 Alcohol also, when not taken in too large quantities, may be oxidized in the 

 body and furnish a not inconsiderable amount of energy. It is, however, a 

 matter of controversy at present whether alcohol in small doses can be con- 

 sidered a true food-stuff, capable of serving as a direct source of energy and of 

 replacing a corresponding amount of fats or of carbohydrates in the daily diet. 

 The evidence is partly for and partly against such a use of alcohol. For example, 

 Reichert l finds that moderate doses of alcohol given to a dog do not affect the 

 heat-production of the body as measured by a calorimeter. Since the alcohol 

 is completely or nearly completely oxidized in the body and gives off consider- 

 able heat in the process, the fact that the total heat-production remains unal- 

 tered indicates that the oxidation of the alcohol protects an isodynamic amount 

 of proteid or non-proteid material in the body from consumption, thus acting 

 as a food-stuff capable of replacing other elements of the food. On the con- 

 trary, Miura 2 has arrived at exactly opposite results in a series of experiments 

 made by another method. In these experiments Miura brought himself into 

 a condition of nitrogen equilibrium upon a mixed diet. Then for a certain 

 period a portion of the carbohydrates was omitted from the diet and its place 

 substituted by an isodynamic amount of alcohol. The result was a loss of 

 proteid from the body, showing that the alcohol had not protected the proteid 

 tissue as it should have done if it acts as a food. In a third period the old 

 diet was resumed, and after nitrogen equilibrium had again been established the 

 same proportion of carbohydrate was omitted from the diet, but alcohol was 

 not substituted. When the diet was poor in proteid, it was found that less pro- 

 teid was lost from the body when the alcohol was omitted than when it was used, 

 indicating that, so far from protecting the tissues of the body by its oxidation, 

 the alcohol exercised a directly injurious effect upon proteid-consumption. 

 Numerous other researches might be quoted to show that the effect of moderate 

 quantities of alcohol upon body-metabolism is not yet satisfactorily understood. 

 Before making any positive statements as to the details of its action it is wise, 

 therefore, to wait until reliable experimental results have accumulated. The 

 specific action of alcohol on the heart, stomach, and other organs has been inves- 

 tigated more or less completely, but the literature is too great and the results are 

 1 Therapeutic Gazette, 1890. 2 Zeitschrift f. klin. Medicin, 1892, vol. xx. p. 137. 



