58 BACTERIOLOGY 



and are found practically everywhere ; others are less common, 

 and some are rare. 



Suppuration is common with the Staphylococci, Streptococci, 

 and Pneumococci, the Pneumobacillus, B. coli, Gonococcus and 

 Meningococcus, M. tetragenus, B. pyocyaneus, etc. ; and is not in- 

 frequent with B. typhosus, B. tuberculosis, B. mallei (the cause 

 of glanders), and various Streptothriceae. 



1. The Staphylococcus group. The commonest and most 

 important member of this group is Staphylococcus (or Micro- 

 coccus) pyogenes aureus, which is widely diffused in nature 

 practically everywhere but especially on the skin and 

 in the mouth, and in the dust of houses. It can therefore 

 readily gain access to a wounded surface. It varies very much 

 in virulence, and may cause anything from the most trivial to 

 the most serious infections. It is the organism most often 

 found in acute abscesses and boils and surface suppurations. 

 One of the most severe infections which is specially liable to be 

 caused by this organism, particularly in young subjects, is sup- 

 puration in or round the bones (suppurative periostitis and 

 osteo-myelitis), which is often in its early stages wrongly 

 diagnosed as rheumatic fever, a very unfortunate mistake, as 

 the condition requires immediate surgical operation. This 

 Staphylococcus is also one of the commonest causes of pyaemia, 

 which used to be a terribly widespread disease in the old days, 

 before antiseptic surgery was introduced, but which is now 

 fortunately comparatively rare. 



Microscopically, the organism is a small round coccus, less 

 than a micromillimetre in diameter, growing in little masses or 

 clusters resembling bunches of grapes, from which it gets its 

 name " Staphylococcus " (see Frontispiece, fig. 1). It stains 

 easily with the ordinary stains. In culture it produces a dull 

 orange-coloured growth from which the descriptive name 

 " aureus " is derived. It grows easily both at room- and at 

 blood-temperature, on all ordinary culture-media, and produces 

 liquefaction of gelatin. It is killed by an exposure of ten 

 minutes to moist heat at 56 or 58 C. 



Other members of this group of less importance are Staphy- 

 lococcus pyogenes albus and citreus, giving a white and lemon- 

 yellow-coloured growth respectively. The former is very 

 common in the skin, and the latter in the throat. 



Many infections due to staphylococci do well with vaccine- 

 therapy, proper surgical treatment being of course also em- 

 ployed. 



2. The Streptococcus group. The commonest pathogenic 

 member of this group is the Streptococcus pyogenes. The Pneumo- 

 coccus is now usually regarded as belonging to the streptococci. 



