An animal fed upon a purely meat diet requires a great amount of it to sustain its body weight. It has been found that from 1/20 to 1/25 of the body weight in lean meat daily is necessary to keep an animal alive without either losing or gaining weight. If more than this amount be supplied the animal increases in weight, and as its weight increases a greater amount of meat is required to keep it up to the new standard. So that, to produce a progressive increase of weight with a purely meat diet, it is necessary to keep on increasing the quantity of meat given. The reason of this is found in the fact that albuminous diet causes an increase in the changes occurring in the nitrogenous tissues.
If an animal which is in extremely poor condition be given an ad libitum supply of lean meat, only a limited portion of the albuminous substance is retained in the tissues. By far the larger proportion of the nitrogenous food is given off and is represented in the urine by urea, and a comparatively small proportion is stored up. If this large supply of meat diet be continued for some time, less and less of the albuminous material is stored, more and more being eliminated as urea, until finally the urea excreted just corresponds to the albuminous materials in the ingesta. When only meat is given, it must be supplied in large quantities to maintain the balance of nitrogenous income and expenditure, which is spoken of as nitrogenous equilibrium. Upon the occurrence of a change in the amount of nitrogenous ingesta this nitrogenous equilibrium varies, and it takes some time to become reestablished, because a decrease in the meat diet is accompanied by a decrease in the weight of the animal, and an increase causes it to put on flesh. For each new body weight there is a new nitrogenous equilibrium, which is only attained after the disturbed relation between the nitrogenous ingesta and excreta has been readjusted.
The increase of weight which follows a liberal meat diet depends in a great measure on fat being stored up in the body. Much more of this material is made than could come from the fat taken with the meat; hence, we must conclude that it is made from the albuminous parts of the meat.
The effect of a diet without any albuminous food is that the animal dies of starvation nearly as soon as if deprived of all forms of food, with the exception that the weight of the body is much less reduced at the time of death.