CHAPTER I. 



THE PROBLEM OF BACTERIAL CLASSIFICATION. 



The question of the systematic relations of the bacteria 

 has been a puzzling one since the earliest days of the 

 science. When these minute forms were first studied 

 by the botanists, Nageli and many other investigators 

 held that pleomorphism and variability were almost 

 absolute among them. Cocci could become bacilli and 

 bacilli, spirilla as the chance of varying environment 

 might dictate. Gradually, however, it has become cer- 

 tain that there are sharp limits to variability even among 

 these simplest of organisms. The study of pathogenic 

 forms in connection with medical and sanitary bacteri- 

 ology has greatly strengthened the conviction that, as 

 a rule, typhoid germs descend from typhoid germs, and 

 tubercle bacilli from tubercle bacilli. The same yellow 

 coccus falls on gelatin plates exposed to the air, all over 

 the world. The same spore-forming aerobes occur in 

 every soil, the same colon bacilli crowd the intestines of 

 animals and men in every clime. These fundamental 

 types cannot be transformed into each other; and the 

 controversy over pleomorphism in its cruder form, as 

 ably presented for example in Migula's System der 

 Bakterien (Migula, 1897) has no vitality today. 



