EXPERIMENTAL INOCULATION. 173 



than in the peritoneum. The virulence of the organism 

 also may vary, and corresponding results may be produced. 

 Especially is this so in the case of the streptococcus pyogenes. 



The staphylococcus aureus, when injected subcutaneously in 

 suitable numbers, produces an acute local inflammation 

 which is followed by suppuration, in the manner described 

 above. The spread of the suppuration goes part passu with 

 the growth of the cocci. Wherever the condition is spread- 

 ing the cocci are present in the tissues at the margin, but 

 after it has ceased to spread they are practically confined 

 to the pus. In the latter case reaction occurs on the part 

 of the connective tissues in the form of cellular proliferation 

 and formation of new capillaries, which lead to the forma- 

 tion of a granulation tissue barrier. After this has been 

 well formed the cocci diminish gradually in numbers and 

 finally disappear. If a large dose is injected, the cocci may 

 enter the blood stream in sufficient numbers to cause 

 secondary suppurative foci in internal organs (cf. intra- 

 venous injection). 



Intravenous injection in rabbits, for example, produces 

 interesting results which vary according to the quantity 

 used. If a considerable quantity be injected, the animal 

 may die in twenty-four hours of a general septicaemia, 

 numerous cocci being present in the capillaries of the 

 various organs, often forming plugs. If a smaller quantity 

 be used, the cocci gradually disappear from the circu- 

 lating blood ; some become destroyed, while others settle 

 in the capillary walls in various parts and produce minute 

 abscesses. These are most common in the kidneys, 

 where they occur both in the cortex and medulla as minute 

 yellowish areas surrounded by a zone of intense congestion, 

 and often haemorrhage. If one of these areas be examined 

 microscopically before actual suppuration has occurred, it 

 will be found that many of the capillaries are filled with 

 cocci, and the tissues immediately around are necrosed, 

 apparently by the action of the products of the organisms. 

 At the margin of the necrosed area there is a dense zone 

 of leucocytes which gradually extend inwards ; ultimately 



