METABOLIC GRADIENTS IN AMOEBA 71 



The exposure of the amoeba to strong cyanide must be re- 

 garded as a strong stimulation ; hence I have thought it advisable 

 to study the reaction of the animal to other strong stimuli. I 

 considered that mechanical stimulation would be the least ob- 

 jectionable and least complicated method of procedure, and 

 therefore have employed as stimulating agent a needle point 

 pressed against the animal with a force sufficient to completely 

 pierce the protoplasm. Both the hay and wheat varieties of 

 amoeba have been used. 



When the amoeba is subjected to such mechanical stimulation, 

 the immediate response is invariable. The stimulated region con- 

 tracts more or less depending upon its previous degree of activity 

 but the most striking effect occurs at the advancing end of the 

 amoeba. This, whether it consist of one or more pseudopodia, 

 contracts powerfully so that its surface is thrown into numerous 

 short projections. The contraction of the anterior end, regard- 

 less of where the stimulus is applied indicates that conduction 

 through the protoplasm is extremely rapid and effective. As a 

 result of this contraction, the protoplasm flows towards the 

 middle of the body which bulges out. (This heaping up of the 

 protoplasm in the center of the body was also observed by Jen- 

 nings, '04, p. 183.) After a little delay, new pseudopodia arise, 

 and the animal moves away in evident haste. The place at 

 which the new pseudopodia appear bears a direct relation to the 

 place to which the stimulus was applied; it is opposite. In this 

 regard strong stimulation differs from moderate or weak stimu- 

 lation which, as Jennings says in the above citation, does not 

 wholly determine the direction of subsequent locomotion. He 

 has however observed that strong stimulation 'may' cause loco- 

 motion in the direction opposite to the point of application of the 

 stimulus, and that strong stimulation applied at the anterior end 

 practically always reverses the direction of locomotion. With 

 this statement I am in complete accord, and to it I must add 

 that when a strong stimulus is applied to any part of the body 

 of the amoeba, the new pseudopodia appear opposite to the place 

 of stimulation. I have experimented with a great many indi- 

 viduals, and have found this response to occur, not perhaps in- 



