THE BEHAVIOR OF INFUSORIA; PARAMECIUM 93 



the infusorian may either react to the more effective of the two, which- 

 ever it is, without regard to the other, or its behavior may be a sort of 

 compromise between the usual results of both. 



If specimens showing the contact reaction are heated, it is found that 

 they do not react to the heat until a higher temperature has been reached 

 than that necessary to cause a definite reaction in free swimming speci- 

 mens. Thus Piitter (1900) found that at 30 degrees C. all the 

 free specimens are strongly affected, moving about rapidly in all direc- 

 tions, while the attached specimens remain quiet or make only slight 

 vibratory movements. Marry of them remain attached until the tem- 

 perature has reached 37 degrees, when the free specimens are dashing 

 about wildly. At this temperature or a somewhat lower one the at- 

 tached specimens become free ; they then dash about as furiously as the 

 others. Thus the contact reaction interferes with the reaction to heat, 

 preventing it until a much higher temperature has been reached than is 

 necessary to cause reaction in free specimens. 



On the other hand, both heat and cold interfere with this contact 

 reaction. Paramecia much above or much below the usual tempera- 

 ture do not settle against solids with which they come in contact, but 

 respond instead by a pronounced avoiding reaction. At a still higher 

 temperature even the avoiding reaction ceases. A Paramecium coming 

 against a solid presses the anterior end against it and continues to try to 

 swim forward, succeeding only in revolving on its long axis (Massart, 

 1901 a). 



Specimens in contact with a solid react less readily to chemicals than 

 do free specimens, so that a higher concentration is required to induce 

 the avoiding reaction. On the other hand, 

 immersion in strong chemicals prevents 

 the positive contact reaction; Paramecia 

 under such conditions coming against a 

 solid react by the avoiding reaction. In 

 this case, then, the effect of the chemical 



is tO change the method of reacting tO FIG. 66. Paramecia which have 



another Stimulus tO the Solid object, formed a ring about a bubble of CO 2 , 

 _ , , . . , , and have then come to rest against the 



Certain other chemicals have the oppo- gi^ supporting rods, forming two 



site effect, favoring the positive contact dense groups- 

 reaction. This is notably true of carbon dioxide. In water contain- 

 ing this substance the infusoria are strongly inclined to settle down 

 against any object with which they may come in contact. They thus 

 often form under these conditions dense masses attached to the glass 

 rods used for holding up the cover-glass (Fig. 66), though usually they 

 do not come to rest against smooth, hard objects. 



