With these facts before us, it is difficult to avoid the conclusion that some significance may attach to the specific nature of the proteid. Of course, we must not overlook the radical difference in dietary habits of man and dog. Man as an omnivorous creature has for generations been accustomed to partake largely of vegetable foods, and as a result his digestive tract and his system as a whole has become acclimated, as it were, to the nutritive effects of vegetable matter. Dogs, on the other hand, are typical carnivores, and their habits for generations have led in an opposite direction, so that their gastro-intestinal tracts and their systems have become accustomed to the effects of a diet in which animal food largely predominates. Whether these deeply ingrained characteristics are responsible in any large measure for the difference in behavior of man, on a purely vegetable diet, and dogs is open to question. It would certainly not be strange if such were the case, but as we look at the facts collected in our study of this subject, it is somewhat impressive to note how well dogs thrive on a relatively large amount of vegetable food, provided there is a modicum of animal food added thereto. In other words, these high proteid consumers are apparently quite able to utilize the vegetable foods, but there is something lacking in such a dietary which the body has great need of. Is it not quite possible, as already suggested, that the specific nature of the proteid counts for something in nutrition? The question cannot be answered definitely at present, but there are certain facts slowly accumulating which make the question a pertinent one in this connection. Thus, it is becoming evident, as was pointed out in an earlier chapter, that the many proteid substances occurring in the animal and vegetable kingdoms are more or less unlike each other in their chemical make-up. They yield different decomposition products, or the same products in widely different proportion, when broken down by the action of hydrolyzing agents; and when we recall that the digestive enzymes of the body convert the proteids of the food into these same end-products, it is plain that in the assimilation and utilization of the proteid foodstuffs the body has to deal with these various chemical units. Hence, an animal suddenly restricted to a dietary in which all of the proteid is furnished by bread might be seriously incommoded, either by the excess of certain amino-acids resulting therefrom, or by a lack of certain other end-products to which its body is accustomed. As an example, we may take the three typical proteids of the wheat kernel, gliadin, glutenin, and leucosin, and note the very striking difference in the proportion of certain of the decomposition products of each, as reported by Osborne and Clapp.[74] [74] See Osborne and Clapp: The Chemistry of the Protein Bodies of the Wheat Kernel. American Journal of Physiology, vol. 17, p. 231.