THE FASTING METABOLISM. 83 
the blood and lymph into the cells of the tissues, while he termed 
the protein of the organized tissues, which is relatively stable and 
but slowly metabolized, organized protein (Organeiweiss). The 
amount of the circulatory protein is small in all cases as compared 
with that of the organized protein, its absolute amount being de- 
pendent, as the above tables indicate and as will appear more 
clearly in the next chapter, upon the supply of proteids in the 
food. Owing to its rapid metabolism, however, it furnishes by 
far the larger part of the nitrogenous waste products in the liberally 
fed animal. 
That the anatomical distinctions implied in the terms used by 
Voit correspond to the actual facts of the case has been disputed 
and may be open to question, but for our present purpose this does 
not particularly concern us. The fact of the existence of the two 
factors of proteid metabolism, viz., a variable one, depending upon 
the previous food-supply and a relatively constant one independ- 
ent of the latter is fully established, by whatever names we may 
choose to call them. 
A Minimum oF Protein INDISPENSABLE.—While the proteid 
metabolism of the fasting animal is speedily reduced to relatively 
small proportions, it is never entirely suspended as long as the 
animal lives. Moreover, to anticipate a portion of the follow- 
ing chapter, even the most liberal supply of non-nitrogenous 
nutrients is pqwerless to suspend or very greatly reduce the pro- 
teid metabolism of a fasting animal. A certain amount of proteid 
metabolism is indissolubly associated with the continuance of life, 
and neither the fat of the body nor the non-nitrogenous ingredients 
supplied in the food can perform these special functions of protein 
in the body. 
§2. Total Metabolism. 
Constant Loss or TrssuE.—Common observation, no less than 
scientific investigation, teaches that a fasting animal suffers a con- 
tinual loss of tissue. Such an animal derives the energy required 
for its vital activities from the metabolism of its store of proteids 
and of fat. As regards the former, we have just seen that in a 
short time, or as soon as the influence of the previous supply of 
