DISEASE GERMS 13 



As to the structure of the bacterial cells but little 

 can be said, except that these simple, unicellular plants 

 consist of a transparent protoplasm enclosed in a cel- 

 lular envelope or membrane. The very varied char- 

 acters which distinguish different species of bacteria 

 make it evident that there are essential differences 

 in the living cell contents, or protoplasm, although 

 these differences are not revealed by chemical analy- 

 sis or by our optical appliances. 



