18 



6. THE ENZYMES IN THE DIFFERENT GROUPS. 



a. Proteolytic enzymes. 



In my introduction I said that the work presented in this 

 paper would not only consist of the study of some new aspects, 

 but also of a checking up of the old data in the literature. 

 This is especially true of the present chapter ; much was known 

 about enzymes in our group already. Nevertheless I have tried 

 to study some as yet obscure points and have come to results 

 different from those of previous authors in one case. 



That there is a proteolytic enzyme present in the starfish, 

 is evident already from its biology. It has more over been 

 found repeatedly already, f. i. by Fredericq 40), C o h n h e i m 

 17), Chapeaux 15) and Griffiths 48). 



Not clear however is the exact relation of radial sac and 

 stomach as far as the secretion is concerned : this question is 

 to be discussed in the chapter on the resorption in the starfishes. 



About the chemical nature of the proteolytic enzyme we are 

 not very well informed either. Here as in almost all groups of 

 invertebrates, we find Krukenberg, who assumes that two 

 enzymes are present simultaneously, i. e. pepsin and trypsin. Roaf 

 and Bourquelot came to the same conclusion. How this is 

 possible, why he assumes the presence of pepsin when the 

 reaction of the digestive juice is on the alcaline side of the 

 neutral point, is not clear. Neither how these two enzymes can 

 act simultaneously while they require an absolutely different 

 hydrogen-ion concentration. All such assumptions of Kruken- 

 berg have been critisised severely by several authors, among 

 which Jordan 65), his ,,Helicopepsin", ,,Isotrypsin" and ,,Ho- 

 maropepsin" have been shown to be fictions. 



His ideas on the simultaneous presence of pepsin and trypsin 

 at the same spot and in the same organ have also been critisised 

 from several sides. In Protozoa, where an acid reaction in the 

 vacuoles preceeds a later stage of alcalinity as first discovered 

 byMetalriikof 83) . , he assumed the same thing. Later investi- 

 gations, like those of Greenwood 47) and Nirenstein 94), 

 have shown clearly, that the acid period only serves for the 

 >t killing" and preparing of the prey, but that no digestion takes 

 place during this time. The digestion and resorption take 

 place in the alcaline period. 



In order to study the nature of the proteolytic enzyme present 

 here a little more in detail, several digests were made. Some 

 of them were acidified with 1.3 pro mille HC1, another part 

 was kept alcaline by means of sodium carbonate. As a sub- 

 strate either gelatin or egg-white raw were added. Of 

 lateral sacs and stomach equal quantities were used; 100 c.c. 

 of water were added in each case and some toluene. 



After four days the digests were taken out of the 37 C in- 



