NOTE ON THE GEOTROPISM OF PARAMECIUM. 



E. P. LYON, 

 PHYSIOLOGY LABORATORY, UNIVERSITY OF MINNESOTA. 



Harper's 1 criticism of my experiment demonstrating, as it 

 seemed to me, that the anterior end of paramecium is the heavier 

 and consequently that the negative geotropism of this animal is 

 an active process was founded upon the assumption that when 

 one begins to centrifuge the animals their geotropism is reversed 

 and becomes positive. Thus the animals start, according to 

 Harper, to move in the direction of the accelerating force and 

 consequently away from the axis of the centrifuge. Harper's 

 experiment by no means proves his contention and it always 

 seemed to me, as Kanda brings out in the foregoing paper, that 

 the quickness with which a high centrifugal force is developed in 

 the centrifuge would prevent the animals from orienting them- 

 selves before they were thrown into the capillary tube where 

 turning is impossible. However, this suggestion might not 

 seem proof to some people; and I have, therefore, performed the 

 following experiment: 



A culture of paramecium was cooled almost to o C. At this 

 temperature they move very sluggishly and show no distinct 

 orientation to gravity. They gather at the bottom of a test tube 

 due, I am sure to the fact that their specific gravity is greater 

 than water and that they make no movement sufficient to keep 

 themselves suspended. The centrifuge was prepared with 

 capillaries such as Kanda and I have used but each one immersed 

 in a larger tube containing ice. A drop of the cold paramecium 

 culture was quickly transferred to the cold capillary tube and 

 centrifuged. The animals were always precipitated with their 

 anterior ends away from the axis. I am quite certain that the 

 animals at this temperature make no reaction to gravity or 

 agitation and that the proof may be considered definite that the 

 head end of the animal is the heavier and that the ordinary 

 geotropic orientation is an active process. 



1 For the literature see the preceding article by Kanda. 



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