20 



N and not about one sixth of what we find in the alcaline 

 digest. Not improbable however is that the trypsin present 

 here should work over a wider range than the trypsin of 

 mammals. 



Another fact which proves that trypsin is at work here, is 

 the regular occurrence of amino-acids in the acid digests : 

 pepsin, as we know, does not carry the hydrolysis any further 

 than up to the peptones. 



In order to make sure that trypsin can work in this degree 

 of acidity, I ran a control in which pure trypsin (M e r c k) 

 was used. After three days already I could demonstrate the 

 presence of peptones and amino-acids, after two weeks I found 

 16 mgr. of non-protein N. 



It does not seem improbable though, that in these lower 

 forms we may have to do with enzymes which do not fit into 

 the classical division of trypsin and pepsin. I have the impres- 

 sion that probably there is a whole series of enzymes, working 

 at very different optima of PH, of temperature etc. 



An interesting paper by Rakoczky 106) has given some 

 experimental evidence for this view. He compares the pepsin 

 of the dog and of the pike. Both had been extracted in exactly 

 the same way, yet there were very decided differences in their 

 activities. Some proteins are attacked more easily by one, some 

 by the other enzyme. On the whole the dog's pepsin has a 

 greater latitude of possibilities. The optimal acidity is higher 

 for the dog's pepsin. Pike pepsin is destroyed much more easily 

 by higher temperatures, on the other hand it stands freezing 

 much better. 



All these properties are extremely purposeful (,,zweckmassig"), 

 from the biological standpoint. It seems as though everywhere 

 such enzymes are present as are necessary or desirable in the 

 conditions. A detailed investigation of the lower forms from 

 this point of view seems very worthwhile. 



In Echinoidea the same proteolytic enzyme is also present, 

 but the enzyme appears very weak here when we compare 

 its action to that of the strong enzyme of the starfish. After 

 eight days no amino-acids could yet be demonstrated, though 

 a peptone-biuret was positive. Later on, especially when dialys- 

 ing tubes were used, they could be demonstrated very easily. 

 R o a f 1 08), Henry 53) and Krukenberg (Toxopneustes) 

 also found a protease in the species they studied. 



In Holothurians the presence of proteolytic enzymes has 

 repeatedly been denied. One of the authors who were not able 

 to find it, in Holothuria tubulosa, is Cohnheim 17). He tried 

 to find it in several different ways, but came to the conclusion 

 that no such enzyme is present. In other chapters that on 



