DEVELOPMENT AND CaMPOSITION OF BACTERIA 9 



and jb he spir al. The rods are known _a s bacilli 

 (sing, bacillus), the spheres as cocci ( sing, coccus), 

 and the sgixafe a^_s£inZfa_(sing. spirillum). More 

 baeciUi are known than any other form, and cocci 

 are much more numerous than spirilla. 



Long-continued growth in artificial media some- 

 times causes abnormal forms of growth, just as 

 unnatural surroundings and conditions produce 

 deformities in the higher forms of life. 



Structure. — The internal structure of bacteria 

 is exceedingly simple : there appears to be a mem- 

 branous covering, including the protoplasm (ger- 

 minal matter), which is not always clearly discern- 

 ible, but in some species (micrococcus of pneumonia) 

 may be seen as a sharply defined capsule inclosing 

 a clear zone. 



The nature of the cell-substance is still imper- 

 fectly understood; the question of the existence 

 of a nucleus and the significance of the internal 

 structure are still disputed points which present one 

 of the exceeding difficulties of which Miiller wrote 

 in 1786. 



Motility. — The power of motion in certain species 

 of bacteria is due to hai Mike appendages , or^aggUa, 

 which by a lashing movement enable them to^mnve . 

 through-fluids* The flagella vary in their position 



