REACTIONS TO HEAT AND COLD. 



gave a brief account of the reactions of Paramecium to heat and cold, 

 according to which these reactions are quite inconsistent with the 

 tropism schema. As the matter is one of considerable interest, and the 

 conclusions reached by Mendelssohn and myself seem quite irrecon- 

 cilable, I have examined anew the phenomena in a considerable number 

 of infusoria, including Paramecium. 



The general phenomena to be explained are well seen in the follow- 

 ing experiment, taken from Mendelssohn (Fig. 3). An ebonite trough 

 10 cm. in length and 2 cm. wide is filled with water containing Para- 

 mecia (a). Now, by proper methods, one end of the trough is slowly 

 heated to 38, while the other is kept at the temperature 26. The 



a 



19- 



19- 



26- 



38'- 



10- 25- 



FIG. 3.* 



Paramecia soon leave the heated region, traveling away from it in a 

 rather compact mass, and in 5 to 15 minutes they have reached the op- 

 posite end (b). If now the temperature at the two ends is reversed, 

 the Paramecia travel back to the end from which they came. If the 

 temperature is lowered to 10 at one end, instead of raised, similar re- 

 sults are obtained ; the Paramecia leave the cold region, as before they 



*FiG. 3. General phenomena of thermotaxis in Paramecium, after Men- 

 delssohn (1902, a). At a the Paramecia are placed in an ebonite trough, both 

 ends of which have a temperature of 19. The Paramecia are equally scattered. 

 At b, the temperature of one end is raised to 38, while at the other it is only 26. 

 The Paramecia collect at the end having the lower temperature ("negative 

 thermotaxis"). At c, one end has a temperature of 25, while the other is 

 lowered to 10. The Paramecia now gather at the end having the higher tem- 

 perature ("positive thermotaxis"). 



