54 



the acidity did not appear ; for this reason I am inclined to 

 believe that this is the source of error in Chapeaux's 

 experiments. 



19. THE NITROGEN METABOLISM OF THE 

 HOLOTHURIANS. 



In his paper on resorption, digestion and metabolism in 

 Echinoderms Otto Cohnheim 17) discusses the nitrogen 

 metabolism of the holothurians. He found no proteolytic en- 

 zyme present in holothurian guts. „Holothuriendarme geben 

 auch nach wochenlangem Stehen an Meereswasser kein Ferment 

 ab, das rohes Fibrin zu losen imstande ist". Fibrin was not dis- 

 solved by such digests in. one day at 37°, if toluene was added. 

 Neither were pieces of mussel changed. Since no glands are 

 present which could secrete a proteolytic enzyme, Cohnheim 

 concludes that there is no such enzyme. Another proof in favor 

 of his view is the negative result of autolysis exf)eriments with 

 Holothuria-guts. This result, namely that autolysis proceeds 

 almost imperceptibly and that such guts can remain unchanged 

 for weeks at a stretch, the present author is prepared to affirm, 

 as mentioned before. 



Other negative results were obtained in experiments on resorp- 

 tion of nitrogenous materials. Ammonia was not resorbed ; in 

 the case of proteins, no protein could be demonstrated at the 

 outside and the total Kjeldahl-N did not increase. 



From these experiments Cohnheim draws the conclusion 

 that „die Resorbtion N-haltiger Korper sehr gering ist, im Ver- 

 gleich mit der reichlichen Resorbtion und Verbrennung von 

 Kohlehydraten, zu gering jedenfalls als dass ich sie erfolgreich 

 untersuchen konnte. Wie und in welcher Form die Holothurien 

 Stickstoffhaltige Nahrung aufnehmen, vermag ich danach nicht 

 anzugeben". 



In our chapter on the enzymes we have seen that a proteo- 

 lytic enzyme is surely present in Thyone. And in the following 

 chapter we have demonstrated that it even occurs in a free 

 form. 



It is clear that these results are in the most evident contra- 

 diction with those of Cohnheim. Theoretically the possibility 

 of course exists, that there may be a specific difference between 

 the two species. Considering the fact, however, that in many 

 other instances we will see that this author has made more or 

 less serious mistakes, I am indined to have my doubts about 

 his results, the more because Enriques 37) found a proteo- 

 lytic enzyme present in the same species on which Cohnheim 

 worked. 



Assuming at first that Cohnheim was right in his experiments, 

 but not satisfied with his attitude of resignation, I studied the 



