62 SCIENTIFIC FEEDING OF ANIMALS 



not more than one-fifth of the protein nitrogen was 

 replaced by gelatine nitrogen. 



If a fully-grown animal is given more protein 

 than it metabolises, when in a state of hunger, it 

 soon puts itself in equilibrium with the amount 

 given, that is, as much protein is destroyed as is 

 present in the food. Where the amount of protein 

 given exceeds that in the preceding feeding the 

 animal, for a time, lays on protein tissue before 

 equilibrium is reached. When, on the other hand, 

 the food has been richer in protein, the reverse 

 is seen, for tissue is lost, until after some time the 

 intake and output become equal. 



Fully-grown animals have clearly not the power 

 of increasing their store of protein, or flesh, beyond 

 certain limits. An examination of the fibres of 

 flesh shows that it is only in youth that they can 

 increase, and that a limit to the increase in thickness 

 is also set. In other ways, too, it is clear that the 

 store of flesh in an animal can only be increased to 

 a small extent. 



The work of which an animal is capable depends 

 in general upon the number of living cells in 

 the body, and if these were intimately dependent 

 upon the supply of food the increase or decrease 

 of body tissue would vary rapidly according to 

 any change of food which might opcur. This, of 

 course, would be entirely opposed to the regular 

 performance of work and resistance to various in- 



