I2O MANUAL OF BACTERIOLOGY. 



Spirilla present a very great variety of form. The short 

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

 although 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. Formerly spirilla without very marked 

 windings were called " vibrios " ; and long, wavy forms 

 with corkscrew-like windings " spirochcetcu " ; and the 

 rigidly spiral forms were denominated " spirilla." These 

 definitions have for the most part lost their significance, 

 although the names still linger in nomenclature. 



FIG. 42. 



Involution Forms of the Spirillum of Cholera. (Van Ermengem.) 



Besides the classification already mentioned, bacteria are 

 sometimes grouped according to certain other qualities. In 

 general botany, saprophytes are plants that grow on decay- 

 ing vegetable matter. In a bacteriological sense, sapro- 

 phytes 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 synon- 

 ymous with the above words are those which do not and 

 those which do produce disease, or non-pathogenic and 



