270 A MANUAL OF BACTERIOLOGY 



vitality of the tissues is depressed, grow and multiply 

 there and produce an abscess. 



The mere presence of micro-organisms does not always 

 induce suppuration ; and the same organism, for ex- 

 ample the Streptococcus pyogenes, may produce a localised 

 abscess, or a diffuse cellulitis, or a pyaemia ; a number of 

 factors control and modify the occurrence and the par- 

 ticular form of septic disease. 



As already mentioned (p. 246), many micro-organisms 

 when injected into the blood-stream are rapidly disposed 

 of ; so when moderate quantities of the Micrococcus 

 pyogenes are injected into the circulation of a rabbit, 

 abscesses, as a rule, form only in the kidney. If, how- 

 ever, the organisms be attached to gross particles, so 

 that they cannot pass through the capillaries, embolism 

 occurs and abscesses form about the embolic foci. The 

 virulence of the infecting organism varies considerably 

 and is another factor of great importance. The pre- 

 dilection of a particular strain of organism to produce a 

 lesion at a particular site has already been referred to 

 (p. 176). The effect of inflammation and injury in making 

 a part " susceptible " is also very marked. Inject the 

 M . pyogenes into animals in which the endocardium or a 

 bone has been damaged, and in all probability an endo- 

 carditis or an osteomyelitis will ensue. Damaged tissues, 

 as occur in lacerated and contused wounds and in gunshot 

 and shrapnel injuries, are particularly vulnerable to infec- 

 tion. Bacterial associations are also important. Thus the 

 B. perfringens grows much more profusely in the presence 

 of micrococci and streptococci, and vice versa. The dose 

 and concentration of the organisms are other important 

 factors. Watson Cheyne found that 250,000,000 cocci 

 (M . pyogenes) injected into the muscles of a rabbit pro- 

 duced a circumscribed abscess, but 1,000,000,000 caused 

 a general septicsemia and death. So, probably, while the 



