EXPERIMENTAL INOCULATION 619 



alhus is responsible for the milder inflammatory lesions, such as acne pustules, 

 stitch abscesses, and other minor suppurative conditions of the skin. Staphylo- 

 cocci are frequently found in conjunction with other organisms, particularly in 

 the chronic stages of gonorrhoea, in bronchitis, in post-influenzal pneumonia, and 

 in catarrhal conditions of the nose and respiratory passages. Their exact signifi- 

 cance in these cases is difficult to assess, but it is probable that they assist these 

 other organisms in giving rise to suppuration. 



Several observers have made personal experiments on themselves to test the 

 pathogenicity of the staphylococci in pure culture. Thus Garre (see Neisser 

 1912) found that by rubbing staphylococci into the skin of his arm he was able 

 to produce boils, which took a considerable time to heal. (For further information 

 on Pathogenicity to man, see Chapter 67.) 



Experimental Inoculation. — The numerous experiments which have been con- 

 ducted on the pathogenicity of the staphylococci suffice to show that the only 

 laboratory animals that can be artificially infected with ease are the rabbit, the 

 mouse, and the guinea-pig. Of these undoubtedly the most susceptible is the 

 rabbit. 



Not all strains are equally pathogenic. As a rule the cocci which are 

 isolated directly from suppurative processes in the body prove virulent, whereas 

 those isolated from skin, air, water, etc., are avirulent. The most pathogenic 

 are the golden strains ; many of the white strains are pathogenic, though to a 

 less degree ; the yellow cocci are generally non-pathogenic. 



Rabbits. — The subcutaneous injection of 1 ml. of a 24-hours' broth culture of Staph 

 aureus gives rise to a local abscess, from which the organisms can be recovered. If the 

 culture is mixed with an equal amount of 2 per cent, melted agar and inoculated intra- 

 cutaneously into the rabbit's back, a spreading necrotic lesion occurs with little pus 

 formation (Jackson, Nicholson and Holman 1940). 



Intravenous injection of 0-1 to 0-5 ml. of a strain oi Staph, aureus recently isolated from 

 a suppurative focus generally proves fatal in 24 to 48 hours. Post mortem, there are 

 haemorrhages and bloody exudations on the serous membranes, and parenchymatous 

 degeneration of the glandular organs ; the cocci can be recovered from the blood 

 stream. 



Intravenous injection of a smaller dose — about 0-01 to 005 ml. — gives rise to a pyaemic 

 condition, accompanied by loss of weight and general weakness, and proving fatal in 

 1 to 6 weeks. Post mortem, multiple small or large circumscribed abscesses are found 

 particularly in the kidneys, and less frequently in the myocardium, lungs, spleen, bone 

 marrow, and costal cartilages. Sometimes vegetations develop on the mitral and tricuspid 

 valves and the chordae tendineae, without any artificial wounding of these structures. 

 Acute osteomyehtis of the long bones not infrequently develops. The cocci can be recovered 

 from the suppurative lesions. In animals that recover, reparative processes occur. 



Staphylococcus alhus is usuaUy much less pathogenic. Strains recently isolated from 

 suppurative foci may cause death on intravenous injection of 1-2 ml. of a 24-hours' broth 

 culture. Strains isolated from saprophytic sources are non-pathogenic unless given in 

 large doses, when death occurs apparently from toxaemia. 



Staphylococci which have been killed by heat at 60° C. for 2 horn's, if given in large 

 doses — 2-4 agar slopes — at repeated intervals of 10 days, may give rise to progressive 

 cachexia with death in 2 or 3 weeks. Post mortem much the same changes are found 

 as those following acute death from a Uving culture, namely a haemorrhagic exudate in the 

 peritoneal cavity, serous haemorrhages, and parenchymatous degeneration of the glandular 

 organs (Koch 1908). 



