370 PEPTONE. [BOOK n. 



proteids are more or less slowly coagulated by alcohol. A useful 

 test for peptone is furnished by the fact that a solution of peptone, 

 mixed with a strong solution of caustic potash, gives on addition 

 of a mere trace of cupric sulphate in the cold a pink colour, 

 whereas other proteids give a violet colour. In applying this test 

 however care must be taken not to add too much cupric sulphate 

 since in that case a violet colour, deepening on boiling, that is the 

 ordinary proteid reaction (see 15), is obtained. 



There are reasons for thinking that there are several kinds 

 or at least more than one kind of peptone ; but we may for the 

 present regard the substance as one. For a long time albumose 

 was confounded with peptone, and many of the commercial forms 

 of " peptone " consist largely of albumose ; indeed the two are 

 closely allied and have many reactions in common, the most 

 striking differences being that peptone is diffusible, while albu- 

 mose is not, or hardly at all, and that peptone is not like albumose 

 precipitated by ammonium sulphate. The amount of albumose 

 appearing in a digestion experiment, relative to the amount of 

 true peptone, depends on the activity of the juice, and other 

 circumstances. We may regard albumose as a less complete pro- 

 duct of digestion than peptone. 



The precipitate thrown down by neutralisation after the action 

 of gastric juice on egg- or serum-albumin resembles, in its general 

 characters, acid-albumin. Since, however, it probably is distin- 

 guishable from the body or bodies produced by the action of 

 simple acid on muscle or white of egg, it is best to reserve for it 

 the name of parapeptone, which was originally applied to it. 



Thus the digestion by gastric juice of solutions of egg-albumin 

 or serum-albumin results in the conversion of all the proteids 

 present into peptone, albumose and parapeptone, of which the first 

 may be considered as the final and chief product, and the other 

 two as intermediate products, occurring in varying quantity, pos- 

 sibly not always formed, and probably of secondary importance. 

 When fibrin, either raw or boiled, or any form of coagulated 

 proteid is dissolved and seems to disappear under the influence 

 of gastric juice, the same products, peptone, albumose and para- 

 peptone make their appearance. The same bodies result when 

 myosin or any of the globulins are subjected to the action of the 

 juice ; and acid-albumin or alkali-albumin is similarly converted 

 into albumose and peptone. 



It is obvious that the effect of the action of the gastric juice 

 is to change the less soluble proteid into a more soluble form, the 

 change being either completed up to the stage of peptone, the 

 most soluble of all proteids, or being left in part incomplete. 

 This will be seen from the following tabular arrangement of 

 proteids according to their solubilities. 



