SUPPURATION AND SEPTIC DISEASES 129 



Pathogenesis. Different strains exhibit considerable 

 variation in virulence. Injected subcutaneously, it 

 forms a local abscess; into the circulation, a septicaemia; 

 into the peritoneum, a purulent peritonitis; and rubbed 

 into the skin, local inflammation, with small pustules 

 (impetigo). Eczema is now generally regarded as being 

 due to the irritative action of the chemical products of 

 8. pyogenes aureus. The organism has been found in 

 ulcerative endocarditis, furunculosis, osteomyelitis, em- 

 pyema, boils, carbuncles, and abscesses, in acne pustules, 

 and occasionally in septicaemia and pyaemia. 



Little or no toxin is formed by 8. pyogenes aureus, and 

 attempts to prepare an antiserum have proved un- 

 successful. Vaccine treatment of staphylococcal infec- 

 tions is, however, quite popular. 



Other Pathogenic Staphylococci. 



Staphylococcus pyogenes albus and 8. pyogenes citreus 

 are not to be distinguished from the aureus variety, except 

 by the colours of the growths on agar or potato. The 

 former produces white and the latter lemon-yellow 

 growths. Andrewes and Gordon regard these three 

 organisms as a single species, owing to their ability to 

 produce intermediate varieties of colour on cultivation. 

 The albus is said to be frequently found in styes. A 

 feebly virulent variety of the S. pyogenes albus is fre- 

 quently present on the skin S. epidermidis albus. Welch 

 finds it to be so deeply buried in the epidermis as to 

 render it difficult to destroy by means of disinfectants. 

 It is the most frequent cause of stitch abscess. While 

 S. pyogenes aureus ferments mannite, with production of 

 acid, this organism has no action. 



Staphylococcus cereus albus forms a greyish-white, 

 wax-like growth, and 8. cereus flavus a wax-like growth, 

 first white, and then yellow, on gelatin. Neither liquefies 

 gelatin. These organisms are specially met with in 

 localised inflammatory conditions, and negative results 

 follow inoculation experiments. 



Micrococcus salivarius, occurring in the saliva, and a 

 micrococcus found in scurf from the scalp, give white 

 growths on agar, and are non-pathogenic for animals. 



