16 BACTERIOLOGICAL INTRODUCTION 



arrangement. The well-known sarcina ventriculi 

 belongs to this group. 



Bacilli. The cylindrical organisms of this group 

 differ from the Cocci in that division takes place in 

 one direction only at right angles to the long axis 

 of the cell so that no forms corresponding to 

 Sarcina or Merismopedia occur. The bacilli vary 

 very greatly in size, B. Anthracis, one of the largest 

 of the pathogenic microbes, being from 3-5 /u long 

 by 1 p wide, while the microbe of influenza has 

 dimensions approximately only the tenth of these. 

 The breadth of the cell is a much more constant 

 feature than the length, as the growth of the cell is 

 in the direction of the long axis. As a rule the 

 cylinder is of equal diameter throughout. Some 

 possess much more rounded ends than others. By 

 division and coherence groups of bacilli are formed 

 which correspond to the diplococci and streptococci 

 of the Coccacese, but these groupings are amongst 

 the bacilli of less constancy, and the names which 

 distinguish them are regarded more as describing 

 varieties of a bacillus than as being the names of 

 sub-groups. The term diplobacillus is not often 

 employed, but might well be used for the organisms, 

 which are by no means uncommon and were formerly 

 described as figure of 8 bacilli (Pasteur). The chains 



