THE BEHAVIOR OF INFUSORIA; PARAMECIUM 65 



This table shows that the relative repellent power of different sub- 

 stances bear a somewhat definite relation to their chemical composi- 

 tion. All alkalies and compounds of the alkali and the earth alkali 

 metals (save the alums, where the proportion of the metals is very small) 

 have a relatively strong repellent effect ; most other compounds have not. 



While our general result is that the stimulating powers of different 

 chemicals are not proportional to their injurious effects, yet one further 

 fact of importance comes out clearly. All substances, whatever their 

 nature, do produce, as soon as they become injurious, the avoiding 

 reaction. With all the substances in the second column the avoiding 

 reaction is produced when a strength sufficient to be injurious is reached 

 and the reaction seems clearly due to the injuries produced. The 

 significance of this fact will be discussed later. 



In the chapter preceding the present one, we have seen that Para- 

 mecia collect in certain chemicals, owing to the fact that passage out 

 of these causes the avoiding reaction. The two chief classes of chemi- 

 cals in which the animals collect are acids and oxygen. 



Paramecia collect in all weakly acid solutions, no matter what acid 

 substance is present. Sulphuric, hydrochloric, nitric, hydriodic, and 

 many other inorganic acids; acetic, formic, carbonic, propionic, and 

 other organic acids, have been tested, and the animals have been found 

 to gather in all. The Paramecia collect even in solutions of poisonous 

 acid salts, such as corrosive sublimate and copper sulphate, where they 

 are quickly killed. In all these cases they swim into the solution with- 

 out reaction, but give the avoiding reaction at passing out. They 

 give the avoiding reaction also after the injurious chemical begins to 

 act on them, but under the circumstances this does not save them from 

 destruction. 



It seems remarkable that the animals should thus tend to gather in 

 acids, when, as is well known, the decaying vegetable infusions in which 

 they live are usually alkaline in character. 

 Specimens in water that is decidedly alka- 

 line collect even more readily in acids than 

 do those iij a neutral fluid. 



A solution may contain both an acid 



and a repellent substance, as when -^ r - per 



cent acetic acid is mixed with J- per cent FIG. 49 . - Collection of Para- 



Sodium chloride. In this Case a CUrioUS mecia about the periphery of a 

 ^(t i. - j JTLT> iU mixture of salt and acid. 



effect is produced. The Paramecia gather 



in a ring about the outer edge of the solution, as in Fig. 49. They are 

 repelled both by the inner fluid and the surrounding water. The path 

 of a Paramecium in such a ring is similar to that shown in Fig. 50. 



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