1 6 TEXTBOOK OF BOTANY 



discovered every year. The majority of them are saprophytes, like 

 the one we have studied. They are found in every conceivable situa- 

 tion — in the air, in both salt and fresh water, 

 » \^ and in the soil. They live in the food we eat, in 



V \ the water we drink, and upon and within many 



\ J parts of our own bodies, as well as of the bodies 



*••» of lower animals and plants. Three classes of 



Fie J. j\ p^g_ bacteria are distinguished which differ from one 



forming bacterium, another in the general shape of their cells ; but 

 Streptococcus pyog- within each class there is considerable variety. 

 enes. Those of one class are nearly or quite globular. 



They form colonies of different kinds, depending 

 upon whether the divisions take place all in the same direction or in 

 different directions. Some of the globular speciesform chains, as for 







^ 



/~\ 



V 



C D 



Fio. 8. — Disease-producing bacteria. A, the bacillus of Asiatic cholera ; 

 B, the bacillus of chicken cholera; C, the bacillus of splenic fever; D, the 

 spirillum of recurrent fever. After Giinther. 



