Activation of the Feeding 

 Reflex in Hydra lift oralis 



HowAiiD M. Lenhoff 



Laboidtories- uf Biochemist nj, Howard Hiiiilies Medical Institute, and 7.oology 

 Department, University of Miami, Mianii, Florida 



Throughout tliis talk, I will often speak of experimenting on 

 Hydra as if these animals were systems of purified enzymes. I 

 speak in these terms more eonfidently toda\' than I could have a few- 

 years ago when I first tried to adapt my former training in enzym- 

 ology to experimentation with live Hydra. In enzymology I was 

 able to treat a relatively simple experimental system in a limited 

 number of ways, and the results were usualh' clear and unambig- 

 uous. I soon found, however, that Hydra could be treated in vir- 

 tually an unlimited number of ways and that the measurable 

 responses of the animal were more difficult to interpret correctly. 



During a rewarding apprenticeship with Dr. Loomis, I was 

 introduced to his method for rearing Hydra in the laboratory in 

 solutions of known composition (16), a development that has en- 

 abled inxestigators to experiment with hydra using the same rigor- 

 ous controlled conditions which are applicable to simpler systems. 

 These first discoveries of Loomis opened the door wide to contem- 

 porary hydra research. 



His selection of Hydra for use in quantitative studies of cellular 

 problems was a happy one because of at least three intrinsic prop- 

 erties of the animal. First, genotypic constancy is practically guar- 

 anteed by using animals descended from a single individual by 

 budding. Second, their small size and lack of skeleton lend 

 them to many of the quantitative techniques (7, 14) applicable 

 to simpler systems. But perhaps the feature of hydra which makes 



20.3 



