THE PYOGENIC COCCI 155 



in twenty-four hours about 500,000,000 organisms per cubic 

 centimeter. They are able to ferment dextrose, lactose, and 

 saccharose, and from them form various acids. Fermentation, 

 however, does not result in the formation of gas. Milk is coagu- 

 lated and indol produced in peptone solution as a result of their 

 growth. 



If a little blood is added to nutrient agar and staphylococci 

 are smeared over it, a clear zone surrounding each colony appears 

 after twenty-four to thirty-six hours' growth; this effect is pro- 

 duced by a hemolytic substance in the organism which dissolves 

 the envelope of the red blood cells and sets free the hemoglobin. 



Resistance. Among the non-spore-bearing bacteria staphylo- 

 cocci are perhaps the most resistant; cultures on gelatin or agar 

 will remain alive for a year or more. Suspended in water the 

 thermal death point varies with different cultures, averaging about 

 two hours at 50 C., one half hour at 60 C., and ten minutes at 

 70 C. They are killed by mercuric chloride 1 in 1000 in from 

 fifteen to thirty minutes, and by carbolic acid 1 in 100 in from 

 twenty to thirty minutes. 



They are very resistant to sunlight, drying, and low temperatures. 



Pathogenesis. Animals appear to be considerably less sus- 

 ceptible than man to staphylococci infections. Large amounts of 

 a pure culture injected into a rabbit may cause the formation of 

 abscesses which generally heal without treatment; or if the 

 culture is sufficiently virulent and a large enough amount be given 

 the animal may die in from two to eight days. On autopsy, 

 abscesses are found in the various internal organs, particularly 

 the liver, kidneys, and in the walls of the heart. These appear as 

 small yellowish masses about the size of a pea surrounded by a 

 zone of intense congestion. Many of the capillaries and smaller 

 arteries are blocked with thrombi consisting of staphylococci. 



Investigators have produced carbuncles in man by rubbing a 

 pure culture of staphylococci upon the unbroken skin. The 

 organisms supposedly gain entrance into the deeper tissues through 

 the base of the hair follicles or sweat ducts. Lowered vitality of 

 the tissues in almost any locality may permit a local invasion 



