PEPTONES. 57 



have been unable to detect any differences between the quantities of 

 nitrogen, carbon, and oxygen, contained in the peptone and in the 

 substance from which it was derived, nor can I infer from my 

 quantitative results, that the conversion of the protein-bodies into 

 peptones is accompanied by an assimilation of water, as might 

 have been supposed. The metamorphosis may be appropriately 

 compared with that of starch into sugar, or even better perhaps, 

 with that of cholic (Strecker's cholalic) acid into choloidic acid. 



I have prepared the peptones either from the natural gastric 

 juice of dogs or from artificial digestive fluid obtained from the 

 pepsin-glands of the stomach of the pig and from coagulated 

 albumen, fibrin, casein, legumin, glutin and chondrin in a state 

 of extreme purity, by allowing them to remain in contact at the 

 necessary, somewhat elevated temperature, till the greater part of 

 the substance to be digested had dissolved; the whole mixture was 

 then boiled and filtered ; the acid fluid was somewhat evaporated 

 over carbonate of lime, and after a second filtration, was con- 

 centrated to the consistence of honey. The addition of alcohol 

 (of 83%) precipitated the lime-and-peptone compound, but dissolved 

 the chloride of calcium ; the undissolved portion, which was very 

 hygroscopical on exposure to the air, and soon ran into a varnish- 

 like mass, was now boiled with absolute alcohol, and was finally 

 extracted, while still hot, with ether containing alcohol. The 

 alkali-compound admitted of being easily prepared from the lime- 

 compound by means of alkaline carbonates. The peptones were 

 obtained nearly, but not perfectly, free from mineral constituents, 

 by carefully removing the baryta, or a great part of it, from their 

 baryta-compounds, by means of sulphuric acid. 



The alkaline carbonates only partially remove lime from the lime- 

 peptone, but they entirely free it from phosphate of lime ; if, for 

 instance, the alkaline peptone-solution after being freed by filtra- 

 tion from the carbonate of lime thrown down by carbonate of 

 potash, be slightly acidified with acetic acid, evaporated and 

 freed from acetates by extraction with alcohol, neither carbonate of 

 soda nor ammonia produces any precipitate when added to the 

 aqueous solution, but a precipitate is caused by oxalate of ammonia ; 

 the ash consists here almost entirely of carbonate of lime. Thus 

 albumen-peptone contains, for instance, 5' 53% of lime. Hence 

 the saturating capacity of albumen-peptone = T67, and its atomic 

 weight = 5960. 



I have obtained perfectly similar results in analysing other 

 peptones, the details of which I shall describe more fully in 



