258 HEAT AND PROTOPLASM [Ch. VHI 



it would contain less water is a question which lacks an experi- 

 mental answer. 



The conclusion from the results offered in this section is 

 this : protoplasm may become so modified through the action 

 of excessive heat or cold that it is no longer killed at the ordi- 

 nary fatal temperatures. This result is partly due to the fact 

 that it is then not so strongly irritated by these extreme tem- 

 peratures, and partly owing to the fact that the coagulation 

 and freezing points have been shifted, possibly through loss 

 of water. 



§ 5. Determination of the Direction of Locomotion 

 BY Heat — Thekmotaxis 



Our knowledge of this subject is still in its infancy and de- 

 pends chiefly upon the observations of Stahl ('84), Ver- 

 WORN ('89, pp. 67-68), Graber ('83 and '87), Loeb ('90, p. 43), 

 DB WiLDEMANN ('94), and Mendelssohn ('95). The first 

 two and the last two mentioned have employed Protista, and 

 we may consider their work first. 



Stahl's studies were made upon Myxomycetes. He used 

 two beakers, of which one was filled with water at 7°; the 

 other with water at 30°. These were placed near each other, 

 and a strip of filter-paper, on which lay the plasmodium of 

 ^thalium septicum, was stretched between them. The two 

 ends of the strip with the corresponding ends of the plasmo- 

 dium hung into the two glasses. The result was that the 

 Plasmodium moved from the colder water toward the warmer, 

 although before the experiment it was moving in the opposite 

 direction. Wortmann ('85) added the observation that when 

 1;he warmer temperature rose above 36° a repellent action of 

 the warmer water was discernible. 



Vekworn experimented chiefly with Amoeba. The difficulty 

 in this operation depended upon the necessity of warming only 

 a part of the body of so small an animal. He used a glass plate 

 of 5 sq. cm. area, to the upper surface of which was glued a 

 piece of black paper, in which had been cut a rectangular open- 

 ing, 3 sq. mm. large, and with very sharp edges. This plate 

 was placed on the stage of the microscope so that the hole lay 



