308 A. A. SCHAEFFER. 



is of course not surprising that soluble objects should be thus 

 sensed, but the sensing of an absolutely insoluble substance at 

 a distance is unique among eyeless animals. It is possible that 

 the carbon grains acted as permanent centers of diffusion of 

 gases adsorbed previously, or adsorption of gases dissolved in 

 the water, and so may have produced differences in their dis- 

 tribution in the water. If these differences in distribution of 

 gases are assumed to come within sensing range of the ameba, 

 then one could understand the observed behavior. I believe 

 however that the gas adsorptive qualities of carbon do not in 

 themselves constitute the stimuli to which ameba reacts when 

 it comes near the carbon; for glass, which is not supposed to 

 adsorb gases to the same extent as carbon, stimulates ameba in 

 a similar manner and quite as markedly. 



Practically all of the behavior toward carbon is positive. The 

 negative behavior observed was due to the commotion produced 

 by placing the carbon in position. In most cases the pseudopod 

 which was sent out to the source of the stimulus, was retracted 

 after it had come into contact with the carbon, but in some cases 

 the ameba flowed on through such an exploring pseudopod. 

 Only in one case was ingestion attempted. That it is a real case 

 of partial ingestion is shown by the fact that the process was 

 incomplete; for if the initial stimulus had come from an un- 

 observed small flagellate, for example, on the carbon grain, it is 

 fairly certain that the ingesting process would have been com- 

 pleted. It is reasonable to suppose that the stimuli causing 

 partial ingestion came from the carbon grain. 



Both granular and raptorial amebas react to carbon at a 

 distance. The raptorial seem to be attracted somewhat more 

 strongly than the granular. 



Glass. Although glass is a complex substance and is very 

 slightly soluble, neither of these properties by themselves play 

 a part in the stimuli received by amebas; for the fragments of 

 glass were taken, in nearly every case, from the dish or slide 

 on which they and the amebas were later placed in experimenting. 

 The effect of its solubility may therefore be thought to have been 

 cancelled physiologically by the solubility of the glass surface 

 on which it lay. 



