THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



67 



most other chemicals the optimum is zero ; an increase in intensity by 

 any effective quantity produces the avoiding reaction, while decrease in 

 intensity has no effect. Hence the Paramecia tend to collect where none 

 of the- chemical is present. 



The point needs to be brought out clearly that it is not merely pas- 

 sage from the absolute optimum that induces reaction, but passage in 

 a direction leading away from the opti- 

 mum. To constant conditions, even when 

 not optimal, Paramecium becomes ac- 

 climatized ; it may live for example in a 

 jJq per cent salt solution, though pas- 

 sage from water to this causes reaction. 

 While in this salt solution, passage into 

 conditions lying still farther from the 

 optimum, as into \ per cent salt solu- 

 tion, causes the avoiding reaction, while 

 passage to conditions lying nearer the 

 optimum produces no reaction. Ac- 

 climatization to non-optimal conditions 

 is an ever present factor in the behavior 

 of the organisms. This is another way 

 of stating the fact that change is the 

 chief factor inducing reactions. 



Acids then take a peculiar position 

 among chemicals merely in the fact that 

 a certain positive concentration forms 

 the optimum, passage to a lower con- 

 centration inducing reaction. The pe- 

 culiar behavior of Paramecium with 

 respect to acids plays a large part in 

 its life under natural conditions. Paramecia produce carbon dioxide 

 in their respiratory processes as do other organisms. This substance 

 when dissolved in water produces an acid solution, the acidity being 

 due to carbonic acid. In such a solution Paramecia gather as in 

 other acids. This may be shown by introducing, by means of a capil- 

 lary pipette attached to a rubber bag containing the gas, a small 

 bubble of carbon dioxide into a slide preparation of Paramecia. The 

 infusoria quickly gather in a dense collection about the bubble, at first 

 pressing closely against it (Fig. 51, ,4). Later the Paramecia spread 

 out with the diffusion of the carbon dioxide (B). After a time the ani- 

 mals are usually found chiefly about the margin of the area containing 

 the carbon dioxide (C). 



Fig. 51. — Collection of Paramecia 

 about a bubble of CO-t. a is a bubble of 

 air, b of CO2. A shows the preparation 

 two minutes after the introduction of the 

 CO2; B, two minutes later; C, eighteen 

 minutes later. 



