f ' 



THE PARENTERAL INTRODUCTION OF PROTEINS 349 



concluded that both homologous and heterologous proteins 

 when parenterally administered are digested and probably 

 assimilated. They say: In fasting animals the parenteral 

 administration of protein leads to increased protein metab- 

 olism. The increased nitrogen elimination is the same 

 whether the injected protein be the serum of the same or 

 of a different species, or egg albumen. In dogs in nitrogen 

 equilibrium protein parenterally administered behaves 

 the same as that given by mouth. Carbohydrates hinder 

 increased nitrogen elimination while on a carbohydrate 

 free diet there is increased nitrogen elimination. In her- 

 bivorous animals (goats and sheep) there seems to be a 

 tendency to retain some of the nitrogen given parenterally, 

 but the results obtained were not constant. We cannot 

 speak of a toxic protein metabolism unless symptoms imme- 

 diately follow the administration. If heterologous proteins 

 be poisonous, when administered parenterally, we have 

 not been able to demonstrate it in fasting animals. If 

 this does not exclude a toxic metabolism it renders its 

 assumption wholly hypothetical. In our experiments 

 increased nitrogen elimination corresponds to increased 

 administration, and a toxic protein metabolism is char- 

 acterized by the fact that nitrogen ingestion and elimination 

 bear no relation to each other. The parenteral adminis- 

 tration of protein has an advantage over the enteral, because 

 in the former we know just how much protein enters the 

 blood. When blood serum is introduced there can be no 

 increased concentration of proteins in the blood, but in 

 fasting animals the introduction of serum, either homolo- 

 gous or heterologous, does lead to increased nitrogen 

 elimination. The transfusion of blood even in large amount 

 from one dog to another is not followed by any marked 

 nitrogen elimination by the recipient. It seems, therefore, 

 that even homologous serum behaves like a foreign protein, 

 possibly on account of the changes that have taken place 

 in it during coagulation. In sensitized animals the parenteral 

 introduction of the homologous protein leads to explosive- 

 like increase in nitrogen elimination. 



