MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 743 



The virulence of the organism shows considerable variation and is 

 usually increased by successive passages through animals of the same 

 species while remaining unaltered for animals of other species. 



Subcutaneous inoculation usually results in abscess formation. 

 Virulent cultures injected into the peritoneal cavity of animals may kill 

 in forty-eight hours to a week or even longer with pysemic abscesses 

 especially in the kidneys. Malignant or ulcerative endocarditis has 

 been experimentally produced by intravenous injection when the heart 

 valves have been injured, chemically or mechanically. Osteomyelitis 

 has also been experimentally produced. 



In man simple rubbing of virulent cultures into the skin is often 

 sufficient to produce a furuncle. 



Upon entering the tissue the cocci are strongly chemotactic and pus 

 inevitably results. With virulent cultures the leucocidal substance is 

 more or less strongly active. The organism may be limited to the first 

 abscess or by invasion of the blood stream multiple abscesses result. 

 In these cases, which are usually fatal, the organism will be found 

 throughout the body. 



Immunization can be secured by repeated injections of cocci dead 

 or alive in graduated doses. The serums possess slight bactericidal and 

 agglutinating properties,, and a high degree of opsonic power. The 

 latter property is probably the most important. 



The serums of immunized animals is protective only when used 

 slightly before or along with, the injection of the organisms and is con- 

 sequently of little practical value. Active immunization, however, is 

 being extensively practised particularly with the autogenous strains. 

 Leucocytic extracts have also been successfully though not so widely 

 used. 



The prophylaxis of staphylococcic infections is the same as for other 

 pus-producing forms. 



Several other kinds of staphylococci have been found associated with 

 pathological conditions, the most important of which are M. pyogenes 

 var. albus, M. epidermidis albus (Welch), and M. pyogenes var. citreus. 

 The first seems to be slightly pathogenic, and rarely produces severe 

 infection. It is distinguished from the aureus by lack of pigment. 



The second variety appears to be an attenuated form of the other. 



The third variety is distinguished from aureus and albus by the 

 development of a lemon-yellow pigment. 



