THE VITAL PHENOMENA OF BACTERIA. 6 1 



bic conditions after parallel cultures which 

 have been freely exposed to air have long 

 since lost their potency. Bunzl-Federn has 

 shown the same thing to be true of the very 

 delicate pneumonia germs. 



Light and Temperature. Sterilization. 



Adaptation to light is developed in different 

 degrees. While most kinds of bacteria thrive 

 in the absence of light others become as it were 

 dormant, and when these latter are brought 

 again into the presence of light an increase of 

 movement sometimes occurs, as has been ob- 

 served by Engelmann. One species indeed 

 showed this sensitiveness to light in so striking 

 a manner that it was named by this observer 

 Bacterium photometricum. On the other hand 

 many bacteria are destroyed by direct sun- 

 light. The existence of any special influence 

 of the presence of bacterial pigment upon 

 behavior to light can as a rule not be demon- 

 strated. 1 In one species containing chlorophyl, 

 Bacterium chlorinum, Engelmann has demon- 

 strated the giving off of a slight quantity of 

 oxygen. Zopf has found also that cultures of 

 the purple bacteria develop more luxuriantly 

 on that side of an aquarium which is turned 

 towards the light. According to Engelmann, 



1 [See, however, Ewart, Journ. Linn. Soc. Bot., 1897, No. 228]. 



r UKIV 



