56 



all doubt. This shows that the products of hydrolysis are 

 also actually resorbed, so that the evidence in favor of my opinion 

 was complete. 



There is still another way of demonstrating the actual resorp- 

 tion and this way is the more biological one. I collected (1) a 

 certain amount of the mud in which the animals are found in 

 nature, (2) a sample of the contents of the fore-gut, -chiefly 

 from the stomach- and (3) one from the end-gut and rectum. 

 These materials were dried for some weeks in an exic- 

 cator, ground up, dried again and finally weighed. After that 

 a total-nitrogen determination was made, based on the principle 

 of the method of Folin. The digestion which could not be 

 carried to completion with Folin- Wu's digestion mixture, became 

 complete after the addition of a little crystal of copper sulfate. 

 In a preliminary experiment I found that direct Nesslerisation 

 was impossible because a heavy precipitate was formed. For 

 this reason the distillation method was used. 



Knowing the amount of material used and the resulting color, 

 it was very easy to figure out the amount of total N in one 

 gram of the three samples. In one gram of the mud as it is 

 found in nature, 3.1 mgr. of total-nitrogen were present, in one 

 gram of a composite sample of each of fore-gut contents as much as 

 21.1 mgr. were present, and in the end gut 1.0 mgr. These 

 figures of course represent samples and do not pretend to have 

 an absolute value, though the samples were of course obtained 

 from many animals. Nevertheless they show very clearly that, 

 at least in certain periods, withdrawal of nitrogenous substances 

 from the mud takes place. The samples 2 and 3 were secured 

 from the same animals, whose fore-gut and rectum were emptied 

 at the same time. 



This withdrawal can be observed even with the naked eye. 

 As long as the material was wet, all samples had the same color. 

 The dried substances showed great diflFerences in color : it was 

 clear, that almost everything present in the stomach sample had 

 been dissolved away except for the sand. 



It will be noted that the quantity of N in the contents of the 

 fore-gut is much higher than that of the mud found in the 

 animal's natural environment. This fact has been explained in 

 chapter 4. 



20. THE RESORPTION IN ECHINOIDEA 

 AND HOLOTHUROIDEA. 



In the chapter on the perivisceral fluid we have compared 

 this liquid to the „blood" in higher animals. The question is 

 whether it actually has the function of transmitting the resorpta 

 from the intestine to the consuming tissue or whether the 

 corpuscles have this function. Cuenot 23) considers the cor- 



