MICRO-ORGANISMS 



a mouse. But the influenza organism is a 

 magnate compared with the yellow fever 

 agent, for this is so small that not one of 

 our wonderful microscopes has yet caught 

 sight of it, and that this is due to its al- 

 most inconceivable minuteness is shown by 

 its passing readily through the pores of a 

 Berkeley porcelain filter which stop the 

 larger bodied organisms of smallpox. 



But the difference in size is a minor mat- 

 ter compared with the great contrasts in 

 vital properties between the various spe- 

 cies of these unicellular forms. A tuber- 

 cle bacillus is in every respect wholly un- 

 like the bacillus of the bubonic plague. 

 The first generally takes months or years 

 before it completes its work, while the 

 other is never chronic, but runs its course 

 in a few days. They differ as much also 

 in their chemical composition and in the 

 chemical accompaniments of their growth 

 on non-living media. Again, some bacilli 

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