PATHOGENIC BACTERIA. 



293 



Culture of the Staphylococcus pyogenes aureus vary con- 

 siderably in virulence. These variations are sometimes to be 

 explained through cultivation on unfavorable media or repeated 

 transplantation from one medium to another; but at times the 

 diminished virulence is due to unknown causes. The lower 

 animals used for experiments are not as 

 readily infected as man. The local intro- 

 duction in rabbits or guinea-pigs of a part 

 of a culture of Staphylococcus pyogenes 

 aureus may be entirely without effect. The 

 use of a very large dose, or the addition at 

 the same time of some kind of irritant, may 

 produce an abscess. Large amounts of 

 cultures in bouillon may often be injected 

 into the peritoneal cavity of the dog without 

 effect, when the simultaneous addition of a 

 piece of sterile potato or an injury to the 

 gut may lead to fatal peritonitis. Intro- 

 duction of fluid cultures into the venous 

 circulation of the rabbit generally produces 

 metastatic abscesses in the kidneys, the 

 heart- muscle and the voluntary muscles, 

 and causes death. 



In man this organism frequently produces 

 suppuration of a merely localized character, 

 such as we are familiar with in boils and 

 carbuncles, but it may also cause gener- 

 alized infection. It has been shown to be 

 the usual cause of infectious osteomyelitis. 

 Osteomyelitis has been produced experimentally in rabbits 

 by the injection of the Staphylococcus pyogenes aureus, both 

 with and without previous injury to the bone which becomes 

 affected. Ulcerative endocarditis has on numerous occasions 

 been shown to be due to this organism. It has been found 



Fig. 66. — Staphylo- 

 coccus pyogenes 

 aureus. Gelatin cul- 

 ture, one week old. 



