244 MANUAL OF BACTERIOLOGY. 



resists drying in a considerable degree. In thq same speci- 

 men the micrococci may have quite different resisting powers 

 to chemical germicides. Some of them are destroyed by 

 i-iooo solution of bichloride of mercury in five minutes; 

 others survive exposure to the same for from ten to thirty 

 minutes. (Abbott.) 



Sterilized cultures introduced into animals may produce 

 local suppuration. The toxic substances occur in the bac- 

 terial cells. 1 



As has already been mentioned, the staphylococcus pyo- 

 genes aureus is the commonest of the pyogenic bacteria 

 in man. It has been obtained from a great variety of 

 sources, and appears to be able to exist as a saprophyte. 

 It has been found on the skin, in the mouth, in the nasal 

 and pharyngeal mucus, and also in the alimentary canal. 

 It has furthermore been detected in the air and in dust. It 

 appears to find the conditions necessary for its existence 

 in the vicinity of human habitations. 



Cultures of the staphylococcus pyogenes aureus vary 

 considerably 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 introduction in rab- 

 bits 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. Introduc- 



1 See also Morse, Journal Experimental Medicine, Vol. I., p. 613. 



