334 Adaptation to Environment 



interpretation the arsenic-fast strain may possibly 

 have existed before the experiments were made, and 

 Ehrlich's treatment consisted only in ehminating the 

 less resistant strains. 



On the other hand, it has been shown that if an 

 arsenic-fast strain of trypanosomes is carried through 

 a tetse fly it loses its arsenic-fastness. This fact may 

 possibly eliminate the applicability of the pure line 

 theory to a discussion of the nature of the arsenic- 

 fastness, but it seems that further experiments are 

 desirable. 



5. Dallinger stated that he succeeded in adapting 

 certain protozoans to a temperature of 70° C. by 

 gradually raising their temperature during several 

 years. It is desirable that this statement be verified; 

 until this is done doubts are justified. Schottelius 

 found that colonies of Micrococcus prodigiosus when 

 transferred from a temperature of 22° to that of 38*^ 

 no longer formed pigment and trimethylamine. After 

 the cocci had been cultivated for ten or fifteen gen- 

 erations at 38° they failed to form pigment even 

 when transferred back to 22° C. Dieudonne^ used 

 Bacillus fluorescens for similar purposes. At 22° it 

 forms a fluorescing pigment and trimethylamine, but 

 not at 35°. By constantly cultivating this bacillus 

 at 35° Dieudonne found that after the fifteenth genera- 

 tion had been cultivated at 35° the bacillus produced 

 * Dieudonn^, A., Arh. a. d. kais. GesndhtsmLf 1894, ix., 492. 



