WEAR AND TEAR QUOTA. 917 



body has become reduced the lower is the protein minimum, according to 



RUBNER. 1 



As mentioned in the early part of this chapter, the body always suffers 

 a certain loss of nitrogen through the falling out of the hair and other 

 epidermis formations, by the secretions, etc.; but to this also belongs the 

 constant loss of nitrogenous substance which every cell sustains because 

 of its activity. This unpreventable loss of nitrogen has been included 

 by RUBNER under the name " wear and tear " quota, and this quota, 

 which corresponds to the nitrogen elimination with a perfectly nitrogen- 

 free diet, and hence is a protein minimum, may rise to 4 to 6 per cent of 

 the total calorific needs. The energy supply of the food is under these 

 conditions entirely assumed by the non-nitrogenous foodstuffs, and when 

 this quota is replaced by protein the body is in a condition of lowest 

 nitrogenous equilibrium. 



All proteins do not have the same value in replacing the protein 

 minimum. MICHAUD 2 determined the protein minimum in dogs by 

 feeding entirely with nitrogen-free food, and he found that this min- 

 imum can be covered by the corresponding quantity of protein specific 

 of the animal, but not by the same quantity of an alien protein, like 

 gliadin and edestin. v. HOESSLIN and LESSER have found on the con- 

 trary in experiments with dogs that proteins specific to the animal were 

 only unessentially superior to the proteins of horse flesh, and E. VOIT 

 and LISTERER found for the three kinds of protein, beef-muscle, aleuronat 

 and casein, that the relation was 100 : 106 : 121. THOMAS 3 has carried 

 out experiments on man with different foods and has found that the 

 nitrogen of various kinds of proteins has an unequal value in replacing 

 the wear and tear quota. By the expression " biological equivalence " 

 of the nitrogenous foodstuffs he denotes the number of parts of body 

 nitrogen which can be replaced by 100 parts of the food-nitrogen and 

 he fourffe the following equivalence: for beef = 104. 7, milk = 99. 7, casein = 

 70.14, wheat flour = 39. 6, potatoes = 78. 9, peas = 55.7, and corn = 29.5. 

 Also in consideration of the different content of nitrogenous extractives 

 in the food these figures therefore show that different proteins have essen- 

 tially different values for the replacement of the nitrogen minimum. 



The purposes of the protein as foodstuff are, according to RUBNER, as 

 follows: (1) To compensate for the wear and tear quota; (2) betterment 

 of the condition of the cells; and (3) dynamogenic purpose. In the 

 accomplishment of this third purpose the protein splits into a nitrogenous 



1 Rubner, Theorie d. Ernahrung nach Vollendung des Wachstums, Arch, f . Hyg., 

 66, 1-80, and Ernahmngsorgange beim Wachstum des Kindes, ibid., 66, 81-126. 



2 Zeitschr. f. physiol. Chem., 59. 



3 v. Hoesslin and Lesser, 1. c., E. Voit and Listerer, Zeitschr. f. Biol., 53; Thomas, 

 Arch. f. (Anat. u.) Physiol., 1909. 



