FEEDING EXPERIMENTS WITH ABIURET PRODUCTS 37 



The same workers later (13) tried to replace the protein in the diet 

 by a mixture of single amino acids, but the attempt was quite un- 

 successful. But little value need be attached to this experiment as 

 many of the amino acids ordinarily found in proteins were absent. 



Henriques and Hansen (187) carried out a series of experiments 

 contemporaneously with much of the German work. They also found 

 that acid decomposition products could not replace protein in the diet 

 although digestion products, which resulted from the long-continued 

 action of trypsin and erepsin, could not only prevent the loss of nitro- 

 gen but could even lead, as Loewi had found, to retention. They 

 further found that the loss of nitrogen could be prevented by feeding 

 with the fraction of the digest products which was not precipitated by 

 phosphotungstic acid, i.e. the monamino acid fraction. They also ob- 

 tained the same result when the products of a tryptic digest soluble 

 in warm 96 per cent, alcohol were used, whereas the alcohol-insoluble 

 products could not prevent loss of nitrogen. The animals which they 

 used for their experiments were rats, and the food in addition to the 

 digestion products contained fat and carbohydrate. The same ob- 

 jection applies here as to Abderhalden and Rona's experiments with 

 mice ; far-reaching conclusions from the metabolism of rats should not 

 be drawn as their nitrogen exchange is too small. But for this objec- 

 tion this piece of work would render the hypothesis put forward by 

 Abderhalden and Rona, that the digestion products are active on 

 account of the higher groups they contain, untenable. The majority 

 of the polypeptides are precipitated by means of phosphotungstic acid 

 and yet the filtrate from this precipitation sufficed to keep the animals 

 alive. 



Sorensen (378), however, has suggested that these positive results of 

 Henriques and Hansen with the monoamino fraction alone were due to 

 this fraction still containing the essential polypeptides which were not 

 precipitated with phosphotungstic acid (Pflaundler (327) has shown 

 that such exist). Sorensen showed that about 20 per cent, of the 

 total nitrogen of the " monoamino fraction " was still in polypeptide 

 form. In a later paper Henriques and Hansen (188) showed clearly 

 that although the products of acid hydrolysis of protein could not 

 replace protein in the diet as efficiently as the products produced by 

 the action of enzymes, they were nevertheless excellent protein 

 sparers, a fact already demonstrated by Henderson and Dean. They 

 concluded, however, from another series of experiments that these same 

 digestion products, if fed along with a protamine (clupeine sulphate), 

 could bring an animal into a state of nitrogenous equilibrium. 



