132 RELATIONS OF BACTERIA TO DISEASE. 



primary lesion, directly or by the lymphatic system, they 

 may become destroyed, or they may settle in certain organs 

 and produce their characteristic effects. The organs speci- 

 ally liable to be affected in this way vary in different diseases. 

 Pyogenic cocci show a special tendency to settle in the capil- 

 laries of the kidneys and produce miliary abscesses, whilst 

 these lesions rarely occur in the spleen. In the spleen, on 

 the other hand, the nodules in disseminated tubercle or 

 glanders are much more numerous than in the kidneys, 

 which in the latter disease are usually free from such. 

 The important point is that the position of the disseminated 

 lesions is not to be explained by a mechanical process, such 

 as embolism, but depends upon a special relation between 

 the organisms and the tissues, which may be spoken of 

 either as a selective power on the part of the organisms or 

 a special susceptibility of tissues, possibly in part due to 

 their affording to the organisms more suitable conditions of 

 nutriment. Experimentally, it has been shown in the case 

 of many organisms that when injected into the circulation, 

 they disappear from the blood in a comparatively short 

 time, and are found in the capillary walls especially in 

 internal organs. Many are destroyed and disappear, but 

 at certain places they may multiply and produce lesions. 

 Even in the case of the lesions produced by dead tubercle 

 bacilli, a certain selective action is found. 



Acute Local Lesions. The local inflammatory reaction 

 presents different characters in different conditions. It 

 may be accompanied by abundant fibrinous exudation, or 

 by great catarrh (in the case of an epithelial surface), or 

 by haemorrhage, or by oedema; it may be localised or 

 spreading in character ; it may be followed by suppuration, 

 or may lead to necrosis. A few examples may be given. 

 A great many different organisms cause an abundant 

 fibrinous exudation. This, along with necrosis of epi- 

 thelium, is the action of the diphtheria bacillus on a mucous 

 membrane, and also of streptococci in certain conditions ; 

 it is produced in the alveoli of the lung in croupous 

 pneumonia by the pneumococcus and probably by other 



