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WEAR AND TEAR QUOTA. 917
body has become reduced the lower is the protein minimum, according to
RUBNBB.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 found 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 Ernahrungsorgange behn Wachstum des Ivindes, ibid., 66, 81-126.
2
Zeitschr. f. physiol. Chem., 59.
1
v. Hoesslin and Lesser, 1. c, E. Voit and Listerer, Zeitschr. f. Biol., 53; Thomas,
Arch. f. (Anat. u.) Physiol., 1909.
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