( 285 ) 



refers principally to the grounds alleged by these two authors for 

 the duality-hypothesis. 



In the first place he has occupied himself with an inquiry into 

 the correctness of the conclusion previously drawn by Bang 4 ) from 

 a number of experiments, that there is not only a difference between 

 pepsin and rennet, but also that even the enzym of rennet does not 

 possess the same qualities in different kinds of animals. Bang con- 

 tinued to apply the old name, chymosin, to the enzym of rennet, 

 as it is found in the calf. From this he distinguished by the name 

 of parachymosin the enzym that can be got from the mucous mem- 

 brane of the pig-stomach. The difference showed itself in the fact 

 that parachymosin, when diluted, became sooner inactive than chy- 

 mosin, that it showed a greater activity by the addition of chlor- 

 calcium, was more proof against heating to 70° C. and less so against 

 the action of alkali. 



With reference to extracts from the mucous membrane of the 

 stomach of calf or pig Gewin could corroborate these differences; 

 only he did not find the difference in the promotion of the activity 

 by adding chlorcalcium as important as Bang. However, it was a 

 different thing, if not the extracts themselves were examined but the 

 enzym extracted therefrom by dialysis, and purified as much as 

 possible in the way formerly communicated by me. The better the 

 purification had taken place, the smaller the difference became. The 

 extract from the mucous membrane of the calf-stomach loses its 

 power to curdle milk when, neutralized, it is heated for 10 minutes 

 to 70° C. ; however, its power is but little reduced, if it is mixed 

 with caustic soda to 0.01 % and neutralized again after half an hour. 

 With the extract of the mucous membrane of a pig-stomach it is just 

 the reverse. With the enzym of the calf, purified as much as possible, 

 the resistance against heating appeared to have become great, against 

 alkali small. From this it must therefore be deduced that the dif- 

 ference does not lie in the enzym itself, but that it is caused by 

 other substances occurring in the extract. Indeed, it could be proved 

 experimentally that the extract from the membrane of the calf-stomach 

 contains substances which protect the enzym against the action of 

 alkali, but make it the more sensitive to heat. Of a solution of 

 purified pig-enzym (which possesses the qualities of Bang's para- 

 chymosin) one half was diluted with water, the other with an 

 extract from the mucous membrane of a calf-stomach, which extract 

 had been deprived of all enzym by heating it for one hour to 80° C. 

 and then neutralized. Of both solutions 2 cc. mixed with 8 cc. of 

 milk caused curdling in 30 sec. A part of each was heated for 



