MICRO-ORGANISMS 



plying in his carefully tended beds. Like- 

 wise our great disinfectants, fresh air, sun- 

 light, and washing, all act by destroying 

 or weakening bacteria by causing changes 

 in their environment unfavorable to their 

 growth. Even the foraminifera find the 

 Arctic seas too cold for them. But not- 

 withstanding all this susceptibility to en- 

 vironment they hold on. The tubercle 

 bacillus, though only seven minutes' ex- 

 posure to sunlight kills him, yet has re- 

 mained the same bacillus for thousands of 

 years, nor once shown a fancy to become 

 an anthrax bacillus nor a cholera vibrio, 

 nor anything else but a tubercle bacillus. 

 It must be some unknown power or prin- 

 ciple of life which first gave origin to these 

 living things and by which they remain the 

 same to-day, yesterday, and for the future. 

 This power or principle of life we can now 

 only designate by the letter X, and many 

 more such Xs we are yet to encounter. 



