464 THE HUMAN BODY. 



cessation of the gain in weight, and an excretion in twenty- 

 four hours of all the nitrogen taken. And so on, until the 

 animal refuses to eat a larger quantity. 



These facts seem, very clearly, to show that proteids can- 

 not be built up quickly into tissues. Meat given to the 

 starving animal has its proteids, at first, used up mainly in 

 luxits consumption while a little is stored as tissue, though 

 at first not enough to counterbalance the daily tissue waste. 

 When a good deal more proteid is given than answers to the 

 nitrogen excretion during starvation, the animal builds up 

 as much into living tissue as it breaks down in the vital 

 processes of these, the rest going in luxus consumption ; it 

 thus neither gains nor loses. Still more proteid if now given 

 does not all appear in the urine at once; some is used to 

 build up new tissue, but only slowly; then, after some days r 

 the increased metabolism of the increased mass of living 

 tissues balances the excess of nitrogen in the diet, and equi- 

 librium is again attained. But, all through, it seems clear 

 that the tissue formation is slow and gradual; and so it be- 

 comes additionally probable that the increased urea excretion 

 soon after a meal is not due to rapidly increased tissue forma- 

 tion and degradation, but to a more direct proteid destruction. 

 The more stable proteid, that which breaks down slowly in 

 starvation and is rebuilt slowly when food is given, has been 

 distinguished as fixed or tissue albumen from the less stable 

 portion, which from the belief that it mainly exists in the 

 liquids of the Body has been named circulating albumen 

 Feeding experiments further show the important fact that 

 the gelatinous or albuminoid foods cannot be converted 

 into fixed proteid; for its formation true albumens are 

 required. The tissues of an animal deprived of all proteid 

 food -stuffs waste, no matter how much albuminoids be given :. 

 but given some of the latter the Body can build tissues and 

 maintain their integrity with less true proteid than would 

 otherwise be necessary, so the gelatin-yielding foods are by 

 no means without nutritive value. 



The Storage Tissues. Every healthy cell of the Body 

 contains at any moment some little excess of material laid' 

 by in itself, above what is required for its immediate neces- 

 sities. The capacity of contracting, and the concomitant 

 evolution of carbon dioxide, exhibited by an excised muscle 

 in a vacuum, seem to show that even oxygen, of which 



