28 PRACTICAL BACTERIOLOGY. 



spiral varies considerably, as does also the thickness 

 of the cell itself. Some of these Spiro-bacteria are 

 exceedingly motile, others are rather inert, whilst yet 

 others are completely motionless. They have been 

 divided into three classes, Spirochoete, Spirillum, and 

 Vibrio, There is, however, no sharp boundary line 

 to be drawn between these classes, as nearly every 

 investigator includes different species under different 

 headings. We shall study the classification of bac- 

 teria more fully in the chapter entitled " Formation 

 of Spores." 



A fourth family of bacteria, the Thread-bacteria, 

 or Desmo-bacteria, is not likely to make its appear- 

 ance. The three most important classes of this 

 family are Gladrothrix, Grenoihrix, and Beggiota. 

 The Beggiota form long, motile threads, consisting 

 generally of colourless cells, and are distinguished 

 by the presence in their cells of numerous strongly 

 refractive granules, which probably consist of sulphur. 

 They occur in sulphur springs, and in dirty water that 

 is rich in decomposing albuminous bodies. 



The class Grenoihrix forms simple threads, the 

 separate cells of which surround themselves with a 

 distinct sheath, and then change themselves by 

 segmentation at their ends into small roundish spores. 

 The threads are motionless, and especially in their 

 younger stages group themselves together into little 

 patches. They are especially frequently found in 



