36 THE PHYSIOLOGY OF PROTEIN METABOLISM 



Henriques and Hansen in Denmark. Abderhalden and Rona (8) 

 carried out a number of experiments on mice using different prepara- 

 tions of caseinogen : 



(1) Caseinogen digested for two months with pancreatin. The 

 preparation gave a faint biuret reaction and contained about 1 5 per 

 cent, of polypeptides. 



(2) Caseinogen digested for one month with pepsin-hydrochloric 

 acid mixture, then for two months with pancreatin. The preparation 

 gave no biuret reaction and contained only about 8 per cent, of poly- 

 peptides. 



(3) Caseinogen hydrolysed ten hours with 25 per cent sulphuric 

 acid. The preparation contained no polypeptides. 



(4) Unaltered normal caseinogen. 



Mice were fed with the various preparations mixed with sugar. 

 Oil was omitted, as when it was present the mice refused the food. 

 They found that the mice fed with preparations (i) and (4) lived about 

 the same length of time. Mice fed on diet (2) died earlier than these 

 but lived longer than mice fed on sugar alone, and mice fed on 

 diet (3) died at about the same time as those fed on sugar alone. 

 Thus it will be noted that the least broken down (15 per cent, poly- 

 peptides) of the digestion products behaved most like the normal 

 caseinogen, that next came the preparation with 8 per cent, of 

 polypeptides, and finally the preparation which to all intents and 

 purposes could not be regarded as a food, the acid product with no 

 polypeptides. This evidence is certainly in favour of the hypothesis 

 that certain nuclei are left more or less intact during digestion in vivo. 

 But experiments carried out on mice can never be regarded as very 

 reliable unless very large numbers of them are used as controls, as the 

 individual differences in the powers of resistance to diet, starvation, etc., 

 are so great that the results of separate experiments are hardly com- 

 parable. Abderhalden and Rona (10) repeated these experiments 

 on a dog, and found unmistakably that part at least of their earlier 

 work on mice was correct. They found that the biuret free digest 

 could completely take the place of protein in the diet, but that the acid 

 hydrolytic product could not do so. In the digest product used in these 

 experiments about 10 per cent, of the nitrogen was in form of poly- 

 peptide. The diet contained both fat and carbohydrates. Abderhal- 

 den and Rona offered as an explanation of their negative results with 

 the acid hydrolytic product, that there had been first a complete disin- 

 tegration of important and necessary compounds, and secondly that 

 racemization of the amino acids had also in all probability taken place. 



