4 Transactions. 



The total nitrogen in meat-extract varies from 6 to 9 per cent. How- 

 ever, in judging the value of an extract it is of importance to consider the 

 forms in which the nitrogen exists rather than its total amount : it has been 

 found by Chittenden* that while the nitrogen-content is high it is not 

 available for the body's use as a food. 



Insoluble proteids should not be present in large amounts : their pre- 

 sence in quantity indicates either the addition of meat-fibre or imperfect 

 methods of manufacture. To add meat-fibre or other pretein to a meat- 

 extract only reduces the proportion of meat bases to which the extract 

 owes much of its true value, and merely adds small amounts of nutriment 

 at an unreasonable price. 



Coaguable proteids are also found i2i small amounts in all meat- 

 extracts. It is impracticable to prepare a meat-extract containing more 

 than a very small amount of coaguable proteids, for the reason that 

 in the process of evaporation the temperature necessary coagulates the 

 proteid. 



Proteoses include the albumoses and certain gelatinoids. Most of the 

 nitrogen attributed to proteoses in meat-extract is due to gelatin or gela- 

 toses, and, as these bodies have a very low nutritive value, f it is apparent 

 that the claim of a high nutritive value for meat-extract rests upon very 

 unconvincing evidence. It is certainly incorrect to suppose that because 

 proteoses are present there must be considerable nutrient property in meat- 

 extract. 



Peptone-like bodies and polypeptides so described in this paper corre- 

 spond with the nitrogen usually determined as and attributed to peptones, 

 but, as the filtrate from the zinc-sulphate precipitate furnished nega- 

 tive results when submitted to the biuret test, it is apparent that no 

 natural peptones are present in the meat-extracts examined. Other 

 investigators have reported a similar experience, and for that reason the 

 absence of peptones in meat-extracts has met with a more or less general 

 acceptance. 



While natural peptones are excluded, it is probable that the nitrogen 

 found in this determination is largely due to the non-biuret-reacting poly- 

 peptides of Fischer,! these substances being intermediate between the 

 peptones and amido acids. 



Fischer has pointed out that the commercial product is very closely 

 related to the natural peptones,, and that peptones are essentially a mixture 

 of polypeptides, and he has further pointed out§ that many of the poly- 

 peptides fail to give the biuret reaction. 



As no true peptones are found in most meat-extracts, it is seen that the 

 claims made concerning the nutrient value of meat-extracts on account 

 of the presence of peptones cannot be substantiated. 



It is to the mineral salts and meat bases that a meat-extract owes its 

 true value. The mineral salts have already been discussed, but it is the 

 meat bases that give meat-extracts their chief value. Their chemistry 

 is most complex ; physiologically the most important are kreatin and 

 kreatinin, and the purin bases. The purin bases usually found are xanthin, 

 hypoxanthin, adenin, and guaiiin. A considerable number of other meat 



* Med. News, 1891, vol. 58, p. 716. 



t Araer. Joiirn. Physiol., 1907, vol. 19, p. 287. 



X " Untersuchungeii iiber Amiiiosauren Polypeptides und Proteinc," p. 23. 



§ Ibid., p. 50. 



