25 PRACTICAL BACTERWLOGY. 



little round cells are grouped iuto thick irregular 

 heaps, they are called Staphylococci; if they form 

 chains, like strings of pearls. Streptococci ; and if they 

 lie together in pairs, Diplococci. All possible sorts of 

 intermediate forms are met with, varying according 

 to their nutriment, or to other similar conditions. 



Quite a different appearance is presented if a drop 

 of putrid-meat infusion be taken up with a loop of 

 platinum wire, and examined in the hanging drop. It 

 is seen to be swarming with active, lively organisms 

 of very various kinds. There are chiefly elongated 

 cylindrical cells, " rod-bacteria," which are sometimes 

 scarcely longer than they are broad, but at others 

 twice, or several times as long, and which occur in all 

 intermediate gradations. There are also great- differ- 

 ences in their thickness ; generally they are about 

 Y^Vo iiam. thick, but they may be either thicker or 

 thinner. Further, we frequently find two or more 

 cells united together to form a chain or thread, being 

 sometimes loosely and at others quite closely con- 

 nected. The rod-bacteria are divided into two classes. 

 Bacillus and Bacterium; it is, however, impossible 

 to draw a sharp line of distinction between them. 

 Generally under Bacillus are included those forms 

 which are more extended, which form, resting 

 spores, and which, as a rule, are motile ; and 

 under Bacterium, those which are shorter, which 

 form no spores, and -which possess no power of 



