3° PRACTICAL BACTERIOLOGY. 



North Germany, and have caused real calamities by 

 stopping up the water pipes. 



Finally, the third class^ Gladrothrix, also forms 

 threads, which possess pseudo-branches ; the separate 

 cells are also enclosed in sheaths ; they are generally 

 found in dirty watei", in refuse water from factories, 

 etc. 



Besides the classes already mentioned, a number of 

 others have been defined ; but as some of these only 

 very rarely occur, and the others may be included 

 under those already mentioned, we need not consider 

 them here. 



After having in this manner learnt to recognise 

 superficially the forms of various bacteria, it is easy to 

 classify them, according to their forms, into four large 

 classes : — 



1. Coccacese, Ball-bacteria. Cells spherical, or 

 shortly eUiptical. (Fig. 2, I.) 



2. Bacteriacese, Rod- bacteria. Cells distinctly longer 

 than broad, straight rods, varying in length. (Fig. 2, 

 11) 



3. Spiro-bacteria (Vibrionacese), Corkscrew-bac- 

 teria. Cells curved, often twisted into long or short 

 spirals. (Fig. 2, III.) 



4. Desmo-bacteria, Thread-bacteria. Cells united 

 to form long threads, some being enclosed in sheaths. 



This system of classification, originated by Ferdi- 

 nand Cohn, is the easiest to use, being the one by 



