THE PROTEINS AND THEIR METABOLISM 117 



Ringer and Dubin in experimenting on a dog weighing 17.0 kg. which 

 fasted for forty-seven days, obtained the following results : 



TABLE V 



During starvation the various processes of life require a certain 

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

 drate (glycogen) 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 

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

 reaches the lowest level that is compatible with life. Landergren calls 

 that the minimal nitrogen metabolism, whereas Rubner views that as 

 representing the "wear and tear" quota. 



Table VI gives the results of a number of experiments by different 

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

 drate and fat diet but free from protein. 



From this table we see that 0.045 grams of nitrogen per kg. of body 

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

 can get along. It represents the "wear and tear" quota. This is an ir- 

 reducible minimum. It corresponds to that part of the protein which can- 

 not be replaced dynamically by any other foodstuff. It is that which is 

 used for the formation of blood corpuscles, hormones, for the growth of 

 bair, skin, nails, epithelial cells, etc. 



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

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

 both proteins and carbohydrates, with all the energy requirements supplied 



