54 



STUDY AND IDENTIFICATION OF BACTERIA 



according to their staining by Gram. The M. tetragenus, S. pyogenes 

 aureus and the pneumococcus stain by Gram, while the gonococcus, 

 the meningococcus, the M. catarrhalis and the M. melitensis are Gram 

 negative. 



M. tetragenus. This organism is frequently found associated with 

 other organisms in sputum, especially with tubercle and influenza 

 bacilli. The colonies are white, slightly smaller 

 than staphylococci and are quite viscid. 



It was formerly considered unimportant in 

 disease, but the idea now prevails that it is re- 

 sponsible for many abscesses about the mouth, 

 especially in connection with the teeth. Injected 

 subcutaneously into mice, it produces a septicaemia 

 and death in three or four days. The blood shows 

 great numbers of encapsulated tetrads. It has been 

 reported twice as a cause of septicaemia in man. 



Staphylococci. To cocci dividing irregularly 

 and usually forming masses which are likened to 

 clusters of grapes the term staphylococcus is ap- 

 plied. While there have been experiments which 

 show that by selecting pale portions of a yellow 

 colony, eventually a white colony could be pro- 

 duced, yet, as a practical consideration, it is con- 

 venient to consider at least two types of staphy- 

 lococci: the Staphylococcus pyogenes aureus and 

 the Staphylococcus pyogenes albus. In culturing 

 from the pus of an abscess or furuncle we generally 

 obtain a golden coccus, while in material from the 

 nose or mouth, the staphylococcus colonies are 

 almost invariably white. As regards the common 

 skin coccus, this will be found to produce a white 

 colony. A coccus which very slowly liquefies gelatin and has been 

 supposed to cause stitch abscesses is the S. epidermidis albus. 



While it is customary to look for a golden colony in the case of organisms show- 

 ing virulence, yet at times a cream-white colony may develop from cocci of great 

 virulence. 



The S. pyogenes citreus is considered as of very feeble pathogenic power. Cer- 

 tain cocci whose colonies have presented a waxy appearence have been designated 

 as S. cereus albus and S. cereus flavus, respectively. They are of very little practi- 



FIG. 12. Gektine 

 culture Staphylococ- 

 cus aureus one week 

 old. (Williams.) 



