BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 305 



Although carbon as thus prepared is quite insoluble, it is not 

 inert, for carbon has the property of adsorbing certain gases 

 from the surrounding medium. In order to render this action 

 as ineffective as possible on the sense organs of the ameba, the 

 carbon grains, which it will be remembered were in all cases 

 microscopic, were immersed in the water in which the ameba was, 

 thirty minutes before being brought near the ameba. It is 

 believed that this period of immersion permitted the adsorptive 

 and diffusive processes to come as near as is possible to an 

 equilibrium. 



A grain of pure carbon was placed in the path of a granular 1 

 ameba (Fig. 42, Plate I.). As the ameba moved forward it 

 turned to the right, but after passing the carbon it turned to the 

 left. After coming into contact with the carbon a pseudopod 

 was thrown out on the right through which the ameba moved 

 away. The same piece of carbon was again laid before the 

 ameba 47 but the behavior was indefinite. 



Several experiments were made on a granular ameba from 

 another culture. A grain of carbon which was laid in its path 

 produced a mild positive reaction: the partial encircling of the 

 carbon 183-188. The carbon grain was then shifted but the 

 commotion caused by moving it led the ameba to react nega- 

 tively. The carbon was shifted again, producing finally a mild 

 positive reaction. When the carbon was shifted again -189 

 the ameba turned to the right. As it passed by the carbon, at 

 about twenty microns, two little pseudopods were sent out in the 

 region of the carbon, one of which was headed directly toward 

 the carbon. The ameba moved directly into contact with the 

 carbon, and then moved on through that pseudopod 193. 



In the path of another granular ameba was placed a grain 

 of carbon 250. The ameba moved on straight forward, passing 

 the carbon on the right. When the ameba was about half past 

 the carbon numerous pseudopods began to make their appearance 

 on both sides of the ameba, before the ameba had come into 



1 See my paper ('16) pp. 533-536, where the granular and raptorial forms of 

 amebas are described. After this paper was in manuscript the specific identity of 

 the amebas was specially examined. The ' granular ' amebas were of two species: 

 Amoeba proleus and A. discoides. The 'raptorial' were of the species A. dubia, 

 See my paper in Science, '16, vol. 44, pp. 468-469. 



