PROTEIN REQUIREMENTS 71 



Jageroos (213) has also investigated the problem whether the 

 organism suffered either directly or indirectly by living on a minimal 

 protein intake. Two pregnant bitches, in both of which the lowest 

 limit of nitrogen exchange was about o - 2 gram per kilo, were studied ; 

 one lived for about ten months and then died suddenly, probably from 

 some infection following abortion ; the other also died suddenly after 

 about six and a half months. (Both animals were on the diet before 

 pregnancy commenced.) In each the food was well utilized through- 

 out, and the general condition continued excellent almost up to the 

 end. He discussed the question whether death was due to lack of 

 resistance towards infection induced by the nature of the diet, or 

 whether the resistance was lowered by the unnatural life (in the cage) 

 and the lack of exercise. (Confinement in cages is frequently ac- 

 credited with producing failure in nitrogen retention.) He concluded 

 that the fatal results were not due to low protein intake, and that 

 the dangers commonly associated with such a scheme of feeding were 

 greatly over-rated, and that if a diet fulfilled all " hygienic" conditions 

 as to amount, digestibility, etc., little attention need be paid to the 

 amount of protein present as long as there is enough to satisfy the 

 tissue needs. 



Quantity or Quality of Protein ? 



It will be shown later (p. 77) that a rapid elimination of nitrogen 

 follows immediately on the ingestion of protein. This being so why 

 should so high an intake of protein be regarded by Voit and others as 

 essential ? What is the real daily protein requirement of the body ? 

 It is evident that the tissues require a fairly abundant supply of protein 

 for purposes of repair, but it is not yet clear what exactly the daily 

 needs are. As has already been pointed out, the tissues evidently 

 exert a certain selective action as in the gliadin feeding experiment. 

 Again, the different tissues differ in composition and presumably re- 

 quire a varying supply of protein in order to satisfy the different repair 

 requirements. As it has not yet been definitely proved that one amino 

 acid can be changed into another if we give a low intake of protein, we 

 may be either starving the animal in whole or in part. To put it in 

 another way, if we remember that the protein molecule is built up of 

 a series of amino acids which for the present we may call A,B,C,D, 

 and so on, and if on a certain day the body requires for purposes of 



