55 



whole question over again. Cohnheim himself states that all 

 nitrogenous excretion takes place through the gut. How is it 

 possible that nitrogen is excreted, if it is not assimilated ? This 

 would mean a constant loss of nitrogen, which we can not 

 understand. That an organism as highly organised as a Holo- 

 thurian should have no nitrogen metabolism seems to be exclu- 

 ded a priori. Growth and formation of proteins are not possi- 

 ble then and yet these substances are present. 



There is still one possibility of error left in Cohnheim's 

 experimental procedure. The work of Enriques has shown 

 that the vasular reticula play a very important role in the enzyme 

 secretion (see chapter 20). One of the enzymes secreted by them 

 is a proteolytic one. If Cohnheim has removed these plexus- 

 ses, he may have missed the opportunity of finding the enzyme. 



In our last chapter we shall discuss the application of Put- 

 ter's doctrine to Holothurians. Thinking of Putter's work 

 and assuming that actually no proteolytic enzyme is present, I 

 made some experiments on the resorption of ammonia and 

 nitrates by Thyone guts. The possibility of the binding of such 

 substances to carbohydrates f. i. as a source of nitrogenous body 

 constituents, should be studied. 



For this purpose I secured Thyone guts. These show the 

 same active movements which mammalian intestine shows in 

 the living organism and move over the table like worms. Pieces 

 were cut out, tied off at one end with a soft, but strong thread, 

 then rilled by means of a hypodermic syringe with the solution 

 to be tested. It was then tied off at the other end with a knot 

 made previously. The loop was now washed sea water and 

 then put into a watch glass in some sea water. 



In this way it became evident that at various concentrations 

 ammonium sulfate diffuses through easily. At the end of the 

 experiment I tested for ammonia in the liquid at the outside 

 with Nessler's reagent and invariably got positive results. 

 The gut was not dead, for very frequently it could still be stimu- 

 lated by pinching it with a forceps. Neither were there 

 leaks since, the liquid did not disappear from the gut though 

 the muscles were in constant tension. 



The same thing holds true for nitrates, for which 

 with the ferrosulfate-sulfuric acid ring reaction. The rate of 

 this resorption is somewhat slower than in the case of ammonia, 

 but most assuredly resorption took place. 



However, we do not have to take refuge in such more 

 or less probable speculations, since there is a proteolytic enzyme 

 and since it is even present in the free form. Amino-acid< 

 diffuse through the intestinal wall, as experiments of the nature 

 of those mentioned above showed. Such experiments were mad 

 with a digest of gelatin by means of trypsin (without toluene 

 A strongly positive ninhydrin-test in the outside liquid took away 



