ROBERT E. EAKIN 409 



was tested. A summary of a study we reported in detail several 

 years ago ( 3 ) states : 



1. Hydra treated with 10 'M lipoic acid for short periods im- 

 mediately after removal of their hypostomes and tentacles com- 

 pletely lose the capacity to regenerate those structures; 



2. Removal of the non-regenerating tip of such blocked hydra 

 leads to relatively normal regeneration; 



3. The blockage of regeneration was found to be reversed in 

 some cases by the action of agents known to interfere with normal 

 nerve activity in more highly developed organisms. 



At that time we postulated that the counteracting effect upon 

 lipoic acid inhibition by certain agents known to depress neural 

 activity in higher organisms was the result of interference with 

 some nerve-mediated reaction which was a vital part of the overall 

 regenerative process. This postulate seemed plausible because of 

 the known involvement of nerves in regeneration of amphibian 

 limbs. It was at this point that Dr. Spangenberg began her histo- 

 logical studies on hydra. In order to get a clear picture of the 

 nerve pattern in untreated and lipoic acid treated hydra, she had 

 to do considerable work in refining the methods then available 

 for staining nerve cells (8). Her intensive and exhaustive studies 

 failed to reveal any observable differences in the nerve cells of 

 regenerating and inhibited organisms. However, her efforts were 

 certainly not wasted because the study not only gave additional 

 information concerning the epidermal nerve net in hydra, but 

 disclosed that it was other type cells that were affected by the 

 lipoic acid treatment. ( Some of Dr. Spangenberg's histological and 

 cytological investigations on the normal and abnormal regeneration 

 of hydra are given on pp. 413-423.) 



ENZYMATIC STUDIES ON A REGENERATION 

 INHIBITOR 



In order to determine whether or not specific phenomena ob- 

 served in hydra were of general significance, we have used other 

 more highly developed systems undergoing morphogenic changes 

 in types of experiments suggested by the results obtained with the 



