8 BACTERIOLOGY FOR NURSES 



inch) in length; the largest (pathogenic) 

 bacterium known is the spirillum (screw-shaped) of 

 relapsing fever ; the bacillus of influenza is one of the 

 smallest of the pathogenic forms, although there are 

 known to be smaller organisms which are too minute 

 to be seen with the present microscopes ; the virus 

 of yellow fever will pass through a porcelain filter ; 

 the germs of pleuro-pneumonia and foot-and-mouth 

 disease in cattle are too small to be observed (ultra- 

 microscopic). 



Shape. The forms of bacteria are exceedingly 

 simple, comprising three types the rod, the sphere, 



/' I 



:;',' 



a b c 



a. Single bacilli. 6. Bacilli in pairs. c. Bacilli in threads. 



oo 

 oo 



a 6 c d e 



a. Staphylococci. 6. Streptococci, c. Diplococci. d. Tetrads, e. Sarcinae 



a b c 



a. and c. Spirilla in comma forms and longer threads known as spiro- 



chaeta. 6. Thick spirals sometimes known as vibrios. 



FIG. 1. 



