SCIENTIFIC PROCEEDINGS. 



Abstracts of Communications. 



Fifty- third meeting. 



Physiological Laboratory , University and Bellevue Hospital Medical 

 College, April 16, IQ13. President Ewing in the chair. 



80 (776) 



Heliotropism and galvanotropism in Euglena. 



By Frank W. Bancroft. 



[From the Department of Experimental Biology of the Rockefeller 

 Institute for Medical Research.] 



Hitherto positively heliotropic Euglena have always been 

 found to give the motor reaction when suddenly shaded, and not 

 when suddenly illuminated. Conversely negatively heliotropic 

 individuals were found to react only to sudden illumination and 

 not to sudden shading. Upon this association Jennings has based 

 his theory according to which heliotropic orientation in Euglena 

 is by "trial and error." 



It has been found, however, that it is possible to obtain posi- 

 tively heliotropic Euglena which give the motor reaction when 

 suddenly illuminated and not when suddenly shaded. It is also 

 possible to obtain at will negatively heliotropic organisms which 

 give motor reactions when suddenly shaded, and not when sud- 

 denly illuminated. Under certain conditions the motor reaction 

 to shading is given by Euglena in which no heliotropism can be 

 demonstrated at that light intensity. Under other conditions 

 distinct negative heliotropism is obtained with a light intensity 

 which does not bring about any motor reactions when allowed to 

 shine suddenly on the organisms, or when they are suddenly 

 shaded. These facts show that heliotropic orientation in Euglena 

 does not depend upon the motor reactions, but upon a separate 

 mechanism. 



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