136 MICRO-ORGANISMS AND DISEASE [chap. 



these again divides into two, either transversely or in the 

 same direction as before. The new elements of succes- 

 sive divisions may remain connected linearly, forming a 

 chain ; or they separate into single organisms or dumb-bells 

 or form smaller or larger connected masses. In some species 

 there is a pre-eminent tendency to form chiefly dumb-bells 

 or diplococcus of Billroth, in others to form shorter or 

 longer chains generally more or less curved, streptococcus 

 (Billroth), and in still others to form connected masses, 

 staphylococcus (Ogston). 



Such exquisite chains one meets with sometimes in serum 

 of blood exposed to the air for some days, and in pleural 

 and peritoneal exudations of animals dead for a few days. 

 I have seen in an artificial culture made by my friend Mr. 

 A. Lingard from a blister in a rabbit's ear the most ex- 

 quisite convolutions of threads of micrococci. Similarly 

 the streptococcus pyogenes and that of erysipelas form in 

 fluid media long, twisted, and convoluted chains. 



In the dividing cocci the single cells are generally more or 

 less crescentic ; this is particularly noticed in staphylococcus 

 aureus and albus and in gonococcus ; it is not marked in 

 others, as in diplococcus pneumoniae and in the streptococci. 



Some species are specially characterised by this that, having 

 divided into a dumb-bell, each of the elements divides again 

 transversely into a dumb-bell, thus forming a group of four 

 (tetrade or sarcinaform). Some species are occasionally 

 met with, particularly in products of air-contamination, in 

 which the four individuals are closely pressed against one 

 another, and then each assumes more or less the shape of a 

 cube, a true sarcina. But each of these cubes divides into 

 four small micrococci arranged as a small sarcina, so that a 

 sarcina-within-sarcina form results (sarcina lutea, sarcina 

 ventriculi). 



