a7id Casein Peptone. 79 



and the length of time the casein is subjected to the action of the 

 ferment. In our earlier work with the proteoses, we deemed it es- 

 sential in attempting a study of the primary products of proteolytic 

 action to use as weak a ferment solution as possible, and to discon- 

 tinue its action as soon as solution of the proteid was complete, in 

 order that there might not be too great a loss through formation of 

 peptone. Further study, however, especially by use of the am- 

 monium sulphate reaction, has shown us that the formation of pep- 

 tone is a far less rapid process than generally supposed. Indeed, in the 

 majority of artificial digestions with pepsin-hydrochloric acid, as or- 

 dinarily conducted, the ammonium sulphate reaction will show the 

 entire absence of peptone. True peptone appears to be formed only 

 by the action of a very vigorous pepsin mixture and that long con- 

 tinued. 



In all of our previous experiments, the casein was either subjected 

 to the action of a very weak pepsin mixture or else, in the use of a 

 stronger ferment, exposed to its action for a few hours only. We 

 now find that by using a far more vigorous pepsin mixture and by 

 continuing its action for several days instead of hours, there is still 

 not a trace of [jeptone to be found in the filtrate from the ammonium 

 sulphate precipitate of the caseoses, but that the caseoses them- 

 selves, particularly the proto and deuterocaseose, differ somewhat, 

 both in composition and reactions from the products previously sep- 

 arated. The discovery of this fact has led us to a further study of 

 the caseoses formed in pepsin digestion, by which we have been able 

 in many ways to verify our former observations and at the same 

 time extend our knowledge of these interesting primary cleavage 

 products of casein. We have also extended our work by studying 

 the caseoses formed through the action of try|)sin, and dilute sul- 

 phuric acid. 



A. Caseoses formed by pepshi-hydrochloric acid. 



In all of these experiments the pepsin mixture was very power- 

 ful, and was especially prepared to insure freedom from both albu- 

 moses and peptone.* The casein was, likewise, thoroughly pure, 

 having been freshly prepared from skim milk by precipitation 

 with 0'2 per cent, hydrochloric acid, and reprecipilation three or four 

 times after ■solution in ammoniacal water. 



* Studies from the Laboratory of Physiological Chemistry, vol. ii, p. 133. 



