634 



PHYSIOLOGY 



protein, probably in the form of increased muscular substance. The amount 

 is too great to be accounted for by retention of the disintegration products of 

 the protein in the body. It must have been stored up in the form of protein 

 and probably, to a large extent at any rate, as actual living tissue. 



In the second experiment the diminution of the protein of the food was 

 followed by a loss of protein from the body, the output being greater than 

 the income. The excess, however, was rapidly diminishing and equilibrium 

 had been practically attained on the last day of the experiment. During this 

 time the animal had excreted 14*8 grm. of nitrogen more than it had received 

 in its food, which would correspond to a diminution of the protein store of its 

 body, reckoned as muscular substance, by 434 grm. Many such experiments 

 have been performed, and they all agree in showing that in carnivora a very 

 appreciable storage of nitrogen can take place in the body. In cats it is 

 sometimes possible to double the body weight by administration of a large 

 protein diet. Since no fat is laid on at the same time and the animals are in 

 a fine healthy condition, one must conclude that the greater portion of the 

 storage takes place by a growth of muscle substance. The degree to which 

 the storage can take place is, however, variable and is generally smaller in 

 dogs than in cats. However much protein is given, the limit is finally arrived 

 at where no further laying on of protein tissues of the body is possible, and the 

 animal then enters into a state of nitrogenous equilibrium, when he excretes 

 a quantity of nitrogen exactly equal to that taken in. This equivalence of 

 income and output signifies that the extent of the total metabolism of the 

 body is affected by the amount of protein supplied in the food, and, as a 

 matter of fact, the total energy output of the body rises and falls with the 

 quantity of protein in the food. This is shown in the Table (p. 635) by 

 Pettenkofer and Voit, in which the figures have been recalculated by 

 Pfliiger. 



We see therefore that carnivorous animals can satisfy their total energy 

 requirements at the expense of protein. When the protein income is in 

 excesss of their requirements a small amount is laid on, probably in the shape 

 of increased muscular tissue. The most marked effect is, however, an 



