41 8 The Biochemical Society, England [June-September 



means of tannln in the presence of salt; and, the albumoses being 

 precipitated by zinc sulphate, the peptones were obtained by differ- 

 ence. For the determination of gelatine, the ice-water-alcohol 

 method of Stutzer was perhaps the most used and most generally 

 considered to give the best results, though some inaccuracy might 

 be caused by the fact that substances rieh in albumoses yielded an 

 appreciable proportion of their nitrogen by this method. 



As to the determination of creatine and Creatinine there seemed 

 little to be said from the chemical side, Folin's method having been 

 thoroughly worked out. The use of ammonium salts had been occa- 

 sionally alleged, but no case of this very crude form of aduheration 

 had come under his notice, though he had met with a sample of 

 extract which, on distillation with magnesium oxide, yielded a con- 

 siderable quantity of ammonia, due, apparently, to some putrefactive 

 change. The residual nitrogen was of ten returned as * meat-bases,' 

 some analysts using for conversion the factor 3.12 originally sug- 

 gested by Stutzer on the basis of the nitrogen percentage of crea- 

 tine. Hehner, however, had suggested the use of the ordinary pro- 

 tein factor of 6.25, which at least had the merit of not involving any 

 assumption or giving to the results an apparent accuracy they did not 

 in fact possess; though on the other band, to those who did not 

 understand the matter, the quantity of 'meat-bases' might be made 

 to appear much larger than it really was, while a considerable error 

 was thrown on the proportion of non-nitrogenous extractives, which 

 was arrived at by difference. The best plan was to retum the actual 

 nitrogen percentages. 



Prof. F. Gowland Hopkins said that the animal body dealt, not 

 with the intact proteins, or even with the albumoses and peptones, but 

 with the free amino-acids, which were the individual constituents of 

 the protein molecule. The actual way in which the different amino- 

 acids were grouped in the protein molecule was not of much conse- 

 quence, but the efifects produced by the individual amino-acids were 

 of extreme importance. He described physiological experiments 

 which he had made showing that when rats were given a diet includ- 

 ing a complete amino-acid mixture corresponding to the proteins of 

 an ordinary diet, their growth was almost exactly normal, while, 

 when arginine and histidine were removed from the amino-acid mix- 



