PAPAIN-PROTEOLYSIS. 165 



biuret test, Nos. 1, 2, and 3 gave a strong reaction for peptone, 

 the reaction in No. 3 being apparently a little the strongest. 

 No. 4, in which the papain was boiled prior to mixing it with 

 the fibrin, gave a purely negative result, thus showing that 

 the peptone reaction in the preceding mixtures could not have 

 come from any admixture contained in the papain itself, nor 

 in the proteid made use of, and that consequently the peptone 

 found must have been formed in some manner during the 

 experiment. Further, this same negative result affords evi- 

 dence that the peptone detected was not formed by putrefac- 

 tion ; hence it must come from the proteolytic action of the 

 enzyme, which is plainly not hindered by the presence of 

 either chloroform, sodium fluoride, or thymol. Lastly, it 

 should be mentioned that the striking brilliancy of the peptone 

 reactions obtained in Nos. 1-3 precludes the possibility of any 

 other conclusion than that a fairly large proportion of true 

 peptone was formed. 



A similar series of experiments was carried out with coagu- 

 lated egg-albumin, 75 grams of the moist coagulum being 

 used in each mixture, with results wholly in accord with 

 those just described. Further, another series in which fresh, 

 thoroughly washed rabbit's muscle (60 grams in each mixture) 

 was digested gave similar results, the only difference being 

 that in Nos. 1-3 the peptone reaction was even stronger than 

 with the coagulated proteids, as might perhaps be expected 

 owing to the easier digestibility of the former. It is thus 

 quite apparent that papain is a true peptone-forming enzyme, 

 and furthermore is able to exert this action upon various 

 kinds of proteid matter. 



What now is the extent to which this formation of peptone 

 may be carried by papain ? In the digestion of proteids with 

 pepsin-hydrochloric acid or gastric juice it has been clearly 

 shown that the formation of peptone rarely exceeds 50 per 

 cent ; proteoses usually predominate.* With alkaline trypsin 



* Chittenden and Amerman, A Comparison of Artificial and Natural 

 Gastric Digestion, together with a Study of the Diffusibility of Proteoses 

 and Peptone. Journal of Physiology, 1893, xiv, p. 483. 



