136 E. R. HOSKINS AND M. M. HOSKINS 



more highly developed than in any other cells in the entire 

 body. They are described in a previous section (see 'Experi- 

 ments'). These cells lining the sinuses are one of the sources 

 of free phagocytes which circulate through the body. Wislocki 

 ('17) does not mention these cells in his discussion of endo- 

 thelial phagocytes in fishes. He states that in no endothelium 

 in fishes has trypan blue been seen except in the lymphatics, 

 renal- and hepatic-portal vessels, and splenic sinuses. He appar- 

 ently would use trypan blue to distinguish between blood-vas- 

 cular endothelium (other than 'specialized' endothelium of the 

 kidney, spleen, and liver) and lymphatic endothelium. He also 

 would use trypan blue to solve the problem of the origin of 

 lymphatics in fishes. We do not believe that trypan blue or 

 other particulate substances can be used in this way. It is 

 highly probable that more extensive research would disclose the 

 fact that the endothelium in various blood-vessels, both arterial 

 and venous, in different parts of the fish's body, is able to ingest 

 trypan blue. The rate at which the dye moves through the 

 vessels is probably one of the most important factors in this, as is 

 believed by Downey ('17). This could be tested by decreasing 

 the rate of blood flow in different vessels with ligatures or other 

 means. Downey ('17) stopped the blood flow^ completely and 

 found that the leucocytes could then ingest dye granules. In an 

 attempt to distinguish between lymphatic and blood-vascular 

 endothelium from the ingestion of trypan blue, one should not 

 set aside all blood-vascular endothelium that is phagocytic to 

 the dye as 'specialized endothelium.' 



Cells in general react toward trypan blue as they do toward 

 other small particles in the circulation and it is not to be used 

 as a specific cure-all for our angiological troubles. Arey ('17) 

 and Downey ('17) have pointed out several ways in which the 

 use of trypan blue has been overdone. 



In our experiments the sinuses in the gills were affected by 

 toxins in somewhat the same way as those in the spleen. There 

 was a proliferation of the endothelium to produce free phago- 

 cytes. Some of these cells stain poorly and in some the cyto- 

 plasm is coarsely granular. There are present in one specimen 



