120 MANUAL OF BACTERIOLOGY. 



occurred. This use is no longer common, although not rarely 

 the name bacterium is still given to a species for instance, 

 bacterium coli commune. 



Spirilla present a very great variety of form. The short 

 " comma- shaped bacilli" are only parts, at most, of spirals, al- 

 though the microbes of cholera do sometimes form long spirals. 

 On the other hand, there are among spirilla large and long 

 sinuous figures which present most remarkable pictures under 

 the microscope; for example, the spirillum of relapsing fever. 

 Spirilla without very marked windings are sometimes called 



FIG. 44. Involution forms of the spirillum of cholera. (Van Ermengem.} 



"vibrios"; and long, wavy forms with corkscrew-like windings 

 "spiroch&ta"j' and only the rigidly spinal forms "spirilla." 



Besides the purely morphological classification already 

 mentioned, bacteria are sometimes grouped according to cer- 

 tain physiological qualities. In general botany, saprophytes 

 are plants that grow on decaying vegetable matter. In a 

 bacteriological sense, saprophytes are bacteria which grow in 

 external nature on dead organic matter, and parasites are 

 bacteria which exist upon the living tissues or fluids of any 

 organism. Nearly synonymous with the above words are those | 

 which do not and those which do produce disease, or non- 

 pathogenic and pathogenic. The adjectives facultative, or 



