128 E. R. HOSKINS AND M, M. HOSKINS 



ability of the urine to reduce copper sulphate after sucrose had 

 been injected demonstrates that the selachians can invert this 

 sugar as mammals do (Kuryama, '16). 



The dogfish kidney was not stained vitally by injected sus- 

 pensions of various dyes, since they were not removed from the 

 blood by the kidney, at least up to five days' time, even when 

 administered in very considerable amounts. There was no 

 difference in this respect between the reaction to very minute 

 particles (trypan blue) or coarse granules (powdered carmine). 

 One sample of neutral red passed through the kidney and one 

 did not do so. The first probably formed a true solution. At- 

 tention of investigators should be called to the fact that some 

 differences they obtain in the use of vital dyes in experiments 

 may well be due to differences in the manufacture of these 

 substances. Colloidal dyes, if impure, may be soluble. 



The inability of the kidney of dogfish to remove particulate 

 matter from the blood is another difference between this organ 

 and the kidney of higher animals, as shown in the very numer- 

 ous experiments of Chrzonszczewski ('64), Siebel ('86), Schmidt 

 ('91), Muscatello ('95), Buxton and Torrey ('06), Suzuki ('12), 

 Hober ('14), Kiyono ('14), Evans-Schuleman ('14), Downey 

 ('17), and many others. 



In higher animals the renal epithelium and sometimes the 

 cavity of the glomerulus may be seen to contain particles that 

 have been injected, but in the dogfish, if such matter is present 

 in the kidney parenchyma or glomeruli, it is much too diffuse 

 to be detected in our preparations. The only dye which really 

 stained the kidneys in our animals was indigo-carmine, and 

 this appeared to be in solution. Fresh kidney tissue was not 

 examined microscopically in the trypan blue experiments, but 

 it probably contained the pink substance that Wislocki noted 

 in teleosts, as the urine was pink. 



The endothelium of the renal capillaries in the dogfish is but 

 poorly able to ingest particulate matter from the blood as com- 

 pared with that of the renal portal vessels of teleosts, as described 

 by Wislocki ('17). Wislocki found that this endothelium becomes 

 blue from ingested dye after injections of trypan blue, while in our 



