PROTEIN REQUIREMENTS 83 



lost, i.e. 3 2 '4 1 grms. Apparently, then, tissue restitution must be 

 a very slow process. Probably if a certain amount of training had been 

 carried out retention would have been more marked. 



In what Form is Protein Retained? 



An observation first made by Voit, and which has repeatedly been 

 verified, seems to be in direct contradiction to this difficulty of protein 

 storage. When the subject, or animal, under investigation is suddenly 

 changed from a protein poor to a protein rich diet the nitrogen output 

 does not immediately jump up to the new protein level ; during the 

 first few days there is less nitrogen excreted than is taken in the food, 

 but eventually nitrogenous equilibrium is established. The same is 

 true when the change is from a protein rich to a protein poor diet, 

 during the first few days succeeding the change more nitrogen is ex- 

 creted than is contained in the food. Two questions naturally rise in 

 connexion with these observations. In what form is the protein or 

 rather the nitrogen retained ? and What is the cause of the retention ? 



The first of these questions has been frequently discussed by Gruber 

 (160), Falta (122), Ehrstrom (in) and others. The general opinion 

 is that the retention takes place in the form of some protein-like 

 material and not in the form of extractives or of end products. The 

 amount of extractive or non-protein nitrogen in the body, however, 

 is by no means an insignificant amount, as Schondorff and others have 

 shown. Thus Schondorff (359) found that the muscle tissue of a 

 22 kilo dog killed after abundant meat feeding contained 40 grms. 

 of nitrogen in the form of extractive bodies soluble in water and that 

 there were from 1 5 to 20 grms. of urea present in the total organism. 



Rubner and Burgi (341 A) have further stated that, in their opinion, 

 part of the nitrogen from meat extract can be retained in the body when 

 the conditions are suitable as, for example, after the administration of 

 the extract at the end of a period of starvation. They found that this 

 retention was always associated with a great retention of water. As a 

 rule, however, the nitrogen of the meat extract was rapidly excreted. 

 Thompson (396) has also shown that a retention of nitrogen given in 

 the form of meat extract can occur. 



The retention certainly does not take place mainly in the form of 

 end or waste products such as urea, as it has been shown that if urea 



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