THE USE OF NILE BLUE SULFATE AS A VITAL 

 STAIN ON HYDRA. 



B. R. WEIMER. 

 HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO. 



In connection with some studies on the reconstitution of Hydra, 

 it occurred to the writer that if some method could be devised 

 for marking the various regions in an animal and if these mark- 

 ings would persist, the process of reconstitution could be followed 

 and interpreted much more easily and accurately. However, in 

 reviewing the literature there seems to be little or no application 

 of any of the so-called vital dyes to the invertebrates, par- 

 ticularly the Ccelenterata. 



Various investigators in studying regeneration in Hydra follow- 

 ing grafting have made use of animals of two different species 

 which differed from each other, among other characteristics, in 

 color. In this way the fate of the graft could be traced. Others 

 have used individuals of the same species which differed from 

 each other in color shade. Both of these procedures are open to 

 criticism in interpretation of results. In the case first mentioned 

 there are undoubtedly present species differences other than 

 color between the animals used, such as differences in the meta- 

 bolic rate of the animal as an individual and differences in 

 gradient patterns. In the second case in individuals of the same 

 species, color differences seem to be indicative of different physio- 

 logical conditions. Observations tend to show, for example, 

 that young Pelmatohydra oligactis (Schulze) Pallas (Hydra fusca 

 L.) are lighter in color than old animals. The same color differ- 

 ence seems to be true of starved animals as compared to fed. 

 From data gathered by various investigators on Tubularia and 

 Planaria, there are marked physiological differences between 

 young and old, and starved and fed animals with respect to 

 metabolic rate and, consequently, capacity for reconstitution 

 under various conditions. Obviously some method of vital stain- 

 ing would remove the necessity for using such methods of mark- 



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