BACTERIA. 



19 



gular masses of bacteria will be formed, the whole growth being 

 in one jelly-like lump. This is termed a zoogloea (Cov, animal, 

 y7Mi6g t glue). 



Locomotion. Many bacteria possess the faculty of self-move- 

 ment, carrying themselves in all manner of ways across the 

 microscopic field, some very quickly, others leisurely. 



Vibratory Movements. Some bacteria vibrate in themselves, 

 appearing to move, but they do not change their place ; these 

 movements are denoted as molecular or " Brownian " and are 

 due to purely physical causes. 



FIG. 2. 



Zoogloea, 



Flagella. Little threads or lashes are found attached to many 

 of the motile bacteria, either at the poles or along the sides, 

 sometimes only one, and on some several, forming a tuft. 



These flagella are in constant motion and can probably be 

 considered as the organs of locomotion ; they have not yet been 

 discovered upon all the motile bacteria, owing no doubt to our 

 imperfect methods of observation. They can be stained and 

 have been photographed. See Fig. 3. Flagella serve some- 

 times to increase food-supply, and have been found on some 

 species which are non-motile. 



