434 SCIENCE PROGRESS 



with three volumes of saturated solution of the salt, suspended 

 the resulting precipitate in water, and subjected it to dialysis, 

 freeing it in this way from much proteid matter which was 

 associated with it. 



The enzyme when thus prepared was found to work in an 

 alkaline medium, but not in an acid one. 



Erepsin, though acting energetically upon peptone, was found 

 capable of decomposing both primary and secondary proteoses 

 also, though the rate of decomposition varied considerably in 

 different cases. 



Cohnheim found that fibrin, coagulated proteids from serum, 

 vitellin from the seeds of the pumpkin, beef, the proteids of 

 the intestinal wall, globin, and the Bence-Jones proteid all 

 resisted the action of the new enzyme. Among the products 

 of digestion he identified, besides the amino-acids occurring in 

 the alimentary canal, the basic bodies argenin, histidin, and 

 lysin. 



Casein appears to be easily and rapidly digested. The 

 position of casein among the proteids is, however, such that 

 this need cause no surprise, and its behaviour does not 

 contradict the view already stated that erepsin acts not on 

 the coagulable proteids proper, but on the products of their 

 digestion. 



Cohnheim's discovery does not stand alone. As we shall 

 see later, investigations made independently on the vegetable 

 proteases by Vines led to the anticipation and subsequent veri- 

 fication of the existence of a peptoclastic enzyme in plants. 

 Vines's work was carried out in large measure before Cohnheim's 

 results were announced, and his experiments were strikingly 

 confirmatory of the latter. 



The discovery of a new enzyme dependent for its activity 

 in the body upon the previous action of other proteases has 

 led to a reinvestigation of the digestive juices. Erepsin seems 

 to share the properties of trypsin, but its discovery at once 

 suggests the question of the real nature of the latter enzyme. 

 It seems at any rate possible that what we have hitherto called 

 trypsin may be a mixture of two enzymes, one peptonising 

 coagulable proteids, the other attacking the peptone when 

 formed. The same question has long disturbed the minds of 

 workers on the hydrolysis of starch, some holding the view 

 that a particular enzyme converts it to dextrin, and a second 



