THE PROTEIXS AND THEIR METABOLISM 



117 



Riniicr ami Piibin in experimenting on a dog weighing 17.0 kg. which 

 fl for fort-seven das, obtained the followin results: 



TAIJLE V 



During', starvation the various processes of life require a certain 

 11 mount of fuel, which is derived from the body's own protein, carbohy- 

 drate (iilycogen) and fat. If the necessary amount of carbohydrate and 

 fat is supplied in the food, but no protein, the individual is kept in. a state 



!' "nitrogen hunger," and after five or six days the nitrogen excretion 

 reaches the lowest level that is compatible with life. Landei-gren calls 

 that the minimal nitrogen metabolism, whereas Rubner views that as 

 representing the "wear and tear" quota. 



Ta hie VI gives the results of a number of experiments by different 

 authors on the urinary nitrogen excretion in man when kept on carbohy- 



Ira re mid fat diet but free from protein. 



l-'n.m this table we see that 0.045 grams of nitrogen per kg. of body 

 \\viijit per twenty-four hours is the minimal amount on which the body 

 'an LM i iil.uig. It represents the "wear and tear" quota. This is an ir- 

 :< -tlueihlc minimum. It corresponds to that part of the protein which can- 

 i' t be replaced dynamically by any other foodstuff. It is that which is 

 u.--ed for the formation of blood corpuscles, hormones, for the growth of 



'air. -kin. nails, epithelial cells, etc. 



It the carbohydrates are also removed from the diet and an isodynamic 

 nuaiitity of fat added, i. e., if an individual is given a diet free from 

 hmli proteins and carbohydrates, with all the energy requirements supplied 



