194 VETERINARY BACTERIOLOGY 



various isolated strains have shown great variation in heat resis- 

 tance. Usually a temperature of 60 for half an hour suffices to 

 destroy all the cells, but some require 80 for the same length of 

 time. The cells are easily destroyed by common disinfectants. 



Pathogenesis. Mechanism of Disease Production. Staphylo- 

 cocci have been shown to produce a leukocytotoxin called leuko- 

 cidin. A stained mount of pus will frequently show that many of 

 the leukocytes have been destroyed, and that the cells are begin- 

 ning to disintegrate. Staphylolysin, a hemolytic toxin, is also 

 produced, particularly by the virulent strains. It seems to have 

 been demonstrated, however, that these two toxins do not explain 

 the pathogenic nature of the organism satisfactorily. Possibly 

 anaphylaxis will explain some of the reactions secured, but there 

 seems to be some poisonous property, possibly an endotoxin, 

 which is not at present understood. We have no satisfactory 

 explanation for its mechanism of disease production. 



Experimental Evidence of Pathogenesis. The causal relation- 

 ship of this organism to pus-production and wound infection has 

 been amply demonstrated. One-tenth c.c. of a twenty-four-hour 

 culture of a moderately virulent strain will kill a rabbit, when 

 injected intravenously, in four to eight days, and, upon post- 

 mortem examination, abscesses containing the same organism will 

 be found in many of the internal organs. 



Types of Natural Infection. As has been stated previously, 

 Micrococcus aureus is most frequently found associated with 

 wound infections, and is also the common cause of abscesses, 

 carbuncles, boils, acne, and furuncles in man and animals, of 

 poll-evil and fistula in the horse, and similar lesions in other animals. 

 The organism may gain entrance to the circulation and produce 

 septicemia or pyemia in man, rarely in animals. It has also been 

 found in man as the cause of certain metastatic infections, par- 

 ticularly of the bone-marrow (osteomyelitis), and ulcerative 

 endocarditis. These have also been produced experimentally in 

 the laboratory animals. Inflammation of the udder in cows 

 (mastitis) is occasionallly caused by this organism. 



Immunity. The production of two specific toxins, the hemo- 

 lytic staphylolysin and the leukocidin, has already been noted, 

 as also the probable importance of an endotoxin. Antitoxins 



