98 Life and Death, Heredity and Evolution 



slowness and gradualness, the animals usually show no ac- 

 climatization ; they die as soon as the temperature or the 

 poison reaches the intensity which was destructive to them 

 at the beginning. But with extreme patience and perse- 

 verance, a change gradually appears. Perhaps the most 

 thorough experiment of this sort ever made was carried out 

 long ago by Dallinger (1887) ; he continued the process of 

 acclimatizing the animals to higher temperature for seven 

 years, and reached more striking results than anyone else 

 has attained. 



Figure 28. Organisms used in Dallinger's experiment on the effects 

 of high temperatures. 1, Monas Dallingeri; 2, Dallingeria Drysdali; 

 3, Tetramitus rostratus. After Dallinger. 



Dallinger worked with three minute flagellates that live 

 in putrefying infusions : Tetramitus rostratus, Monas Dal- 

 Imgeri, and Dallingeria Drysdali (see Figure 28). The 

 temperature at which they flourished was 60 F. (16 C.); 

 they were killed at once by a temperature of 142 F. (61 

 C.). But at least one of them, Dallingeria, formed spores 

 which could resist (in fluids) a temperature of 220 F. 

 (104 C.). 



Dallinger undertook to accustom the animals to higher 

 temperatures. He found that up to 70 F. little difference 

 was observable in the life and growth, although the animals 

 lived better under the later increases if the change from 60 

 to 70 was made very slowly. Above 70 it became neces- 

 sary to proceed with extreme slowness ; Dallinger raised the 



