THE BEHAVIOR OF INFUSORIA; PARAMECIUM 101 



a temperature optimum of about 24 to 28 degrees ; if they are kept for 

 some hours at a temperature from 36 to 38 degrees, the optimum rises 

 to 30 or 32 degrees (Mendelssohn, 1902). A change in the individuals 

 induced in this way is commonly spoken of as acclimatization. Simi- 

 lar changes could doubtless be induced in the reactions to chemicals 

 and to other stimuli ; this has not yet been done. 



Paramecia that have long been deprived of food behave in a some- 

 what different manner from normal individuals (Moore, 1903; Wal- 

 lengren, 1902 a}. But the changes in behavior are apparently due to 

 actual structural changes in the organism, due to lack of food, and render- 

 ing it impossible for the animal to move so strongly and rapidly (Wal- 

 lengren, 1902 a). Paramecia kept in distilled water are found to be 

 much more sensitive to most stimuli than usual (Jennings, 1897 ; Wal- 

 lengren, 1902 a); owing apparently to lack of sodium salts in the body. 

 This condition may perhaps be called that of salt hunger. If a small 

 quantity of some sodium salt is added to the distilled water, the Para- 

 mecia return to the usual condition (Wallengren, 1902 a). 



Certain changes in the behavior of individuals can hardly be classi- 

 fied as due either to fatigue, acclimatization, or hunger. If a bit of 

 filter paper is placed in a preparation of Paramecia, the following be- 

 havior may often be observed. An individual swims against it, gives 

 the avoiding reaction in a slightly marked way, swimming backward 

 a little; then it swims forward again, jerks back a shorter distance, 

 then settles against the paper and remains. After remaining a few 

 seconds, it may move to another position, still remaining in contact 

 with the paper. Then it may leave the paper and go on its way. All 

 this may happen without the slightest evident change in the outer con- 

 ditions. So far as can be seen, the Paramecium first responds to the 

 solid by the avoiding reaction, later by the positive contact reaction, 

 and still later suspends the contact reaction, all without any change in 

 external conditions. The changes inducing the change in reaction must 

 then be within the animal. 



Again, as we have seen, jarring Paramecia which have collected at 

 the top of a tube often causes them to swim to the bottom of the tube 

 (Sosnowski, Moore). The jarring itself lasts but a moment, while 

 the Paramecia continue for some time after to swim downward. The 

 shock must therefore have changed the physiological condition of the 

 animals, so that they now show a change of reaction to gravity, or 

 possibly a lack of reaction to gravity. 1 



1 It is possible that the shock merely causes them to swim rapidly in any direction 

 that is open to them. Since they are already at the top of the tube, the only direc- 

 tion open to them is that leading downward. 



