272 A MANUAL OF BACTERIOLOGY 



peptone water it gives the indole reaction with the addi- 

 tion of a nitrite, but not without. 



The rate of liquefaction of gelatin and the pigment 

 production vary ; the latter is sometimes much deeper 

 than at others, recently isolated cultures show it better 

 than old ones, and the presence of oxygen also seems to 

 be necessary. The amount of acid production appears 

 to vary directly with the virulence, which is likewise very 

 variable. 



Pathogenicity . The Micrococcus pyogenes, var. aureus, 

 is by far the commonest of all organisms met with in 

 suppurative processes. Ogston found it alone in thirty- 

 four, and associated with the Streptococcus pyogenes in 

 sixteen, out of sixty-four cases of abscess. It occurs in 

 acute abscesses, boils, and acne, in some cases of puer- 

 peral fever and infective endocarditis, and is almost 

 invariably found in osteomyelitis, but only occasionally 

 in pyaemia. The organism injected under the skin of 

 man or animals produces an abscess, and injection into 

 the blood-stream under certain conditions is followed by 

 infective endocarditis or by pyaemia. Impetigo pustules 

 are produced by inunction of culture into the skin. 



It may be said to be universally present on all parts 

 of the skin, and in the mouth, and is frequently met with 

 in the air. According to Sternberg, recent cultures in 

 gelatin are destroyed by an exposure to a temperature of 

 56 to 58 C. for ten minutes ; but when dried much 

 higher temperatures, 90 to 100 C., are required, and in 

 the dried state (on a cover-glass) it retains its vitality for 

 more than ten days. According to different experi- 

 menters, from five to fifteen minutes are required to 

 destroy it with a 11,000 mercuric chloride solution ; but 

 it is evident that much depends on the state of aggregation 

 of the organisms. 



Toxins. In a case of infective endocarditis examined 



