[Illustration: _Subject No. 17._ _January 2, 1906_] [Illustration: _Subject No. 17._ _February 27, 1906_] [Illustration: _Subject No. 17._ _April 24, 1906_] [Illustration: _Subject No. 17._ _June 27, 1906_] This is by no means an exceptional case, but we can cite many other examples of like results where the animal when restricted to a purely vegetable diet, such as bread, pea-soup, bean soup, etc., reinforced by an animal fat, quickly passed from a condition of health into a state of utter wretchedness, with serious gastro-intestinal disturbance. The results are not to be attributed to the lower utilization of the vegetable food, for the disastrous effect is too quickly manifest, and further, often shows itself when the animal plainly has a large store of available nutriment in its own tissues. This experiment with dog No. 17 has been dwelt upon at some length, because it illustrates a very important principle in the nutrition of a high proteid and carnivorous animal. As before stated, it is not a question of high or low proteid simply, but involves possibly the more subtle question of the relative value of specific forms of proteid food. It will be noted that this statement is made somewhat guardedly, in harmony with the caution necessarily called for in view of our lack of knowledge regarding the possible need of the animal’s body for extraneous principles which only meat, milk, or other animal products can supply. Inorganic salts, nitrogenous extractives, and other substances without any appreciable fuel value, are quite likely to be of primary importance in controlling and regulating the various processes of the body, which combine to maintain the condition of normal nutrition. With a diet restricted to one or two vegetable products, it is quite conceivable that something may be lacking which the system demands, though it cannot be measured in terms of nitrogen or calories. It may be said that man thrives on a purely vegetable diet, but while this is unquestionably true, it must be remembered that man with his free choice of food has recourse, as a rule, to a large variety of vegetable products from many sources, and consequently there is great likelihood of his absorbing from these varied products such supplementary matters as may be needed. On this question, we are in a realm of doubt and uncertainty, but the possibilities suggested must not be ignored, for they may contain a germ of truth of the utmost importance. The fact remains, however, that a dog when restricted to a purely vegetable dietary does not thrive; a little animal food seems necessary to keep up health and strength, and this suffices even though the daily nitrogen intake and fuel value of the food are restricted to a level below that of the vegetable dietary.