PHYSIOLOGY 



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riod" is more than twice (up to ten times) that of a single animal in 

 the same amount of the medium. He assumed that this acceleration 

 was due to a certain agent or substance produced within the animal, 



Fig. 40. Didinium nasutum, X265 (Beers), a, normal fully grown ani- 

 mal; b-e, abnormal organisms which were fed on starved Paramecium. 



which diffused into the culture medium. When more than one animal 

 is confined in a limited amount of culture fluid, this substance is 

 present in a higher concentration than with one animal, and an in- 

 creased rate of division is the result. Robertson called this "allelo- 

 catalytic result," and the phenomenon, "allelocatalysis." 



