REACTION OF SELACHII TO INJECTIONS 129 



animals up to five days only an occasional one of these cells 

 was able to take in visible amounts of carmine or trypan blue. 

 It is possib'e that after a greater length of time this endothelium 

 in dogfish would react as does that of teleosts toward trypan 

 blue. Wislocki also found a small amount of dye in the epithe- 

 lium of the kidney in teleosts. This he believed might have 

 been resorbed from the urine. Previous investigators have 

 agreed with him (Cushny, '17). He also implies that the 

 endothelium of the vessels in the kidney developed from the 

 aorta is not able to take in and store trypan blue, but it is 

 difficult in microscopical sections to distinguish the efferent 

 glomerular vessels from renal-portal vessels. 



Wislocki suggests three possible functions of the renal-portal 

 endothelium in the kidney which he calls a mechanism. The 

 first function is to prevent loss of colloidal metabolites, thus 

 accounting for the relatively low output of nitrogen in fish 

 urine, but the real reason for this is probably in the slow rate of 

 metabolism in fish and a large output of nitrogen in the bile. 

 The second function Wislocki attributes to the renal-portal 

 endothelium is to protect the animal from toxic substances, but 

 in an animal not being experimented- on, any toxic substances 

 present would more likely be in solution than in suspension, and 

 solutions pass freely through the kidney. The third function 

 referred to is a resorption of substances from the urine, but the 

 reaction to trypan blue does not prove any such function, as it 

 has not been shown that in these experiments the endothelium 

 in question absorbed dye in this way. The possibility of such 

 resorption of dyes has been considered previously, as noted 

 above. All that Wislocki' s experiments actually prove is that 

 the endothelium of the renal vessels is phagocytic, but not very 

 permeable, if permeable at all, to particulate matter. 



The liver excretes particles freely, but whether such function 

 failed to develop in the kidney because of this fact or whether 

 the inability of the kidney to excrete particulate matter forced 

 the liver to develop the function cannot be determined. Nor- 

 mally, particles in the circulation which are to be eliminated are 

 mostly bile pigments which of course need not go into the urine. 



