710 



PHYSIOLOGY 



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 adminis- 

 tration 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 con- 

 clude 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 following Table 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 excess of their requirements a small amount is laid on, 

 probably in the shape of increased muscular tissue. The most 

 marked effect is, however, an increased metabolism which rises in 

 proportion to the nitrogenous income. The limit to this increase is 

 set by the powers of the alimentary canal to digest the protein. The 

 rise in metabolism^ consequent on protein food is very rapid and 

 affects the gaseous exchanges as well as the output of nitrogen. 

 Magnus Levy and Falk found that a large protein meal might 

 increase the respiratory exchanges 40 per cent., an increase which 

 lasted seven hours. The nitrogenous output also rises immediately 

 after a protein meal, so that 50 per cent, of the nitrogen of the ingesta 

 may appear in the urine within seven hours after the meal. 



