LOCAL LESIONS 157 



agent, but it must still be held as uncertain whether the process 

 of exudation ought to be regarded as primarily defensive or as 

 the direct result of damage to the endothelium of the vessels. 

 It may also be pointed out that the various changes referred to 

 are none of them peculiar to bacterial invasion ; they are examples 

 of the general laws of tissue change under abnormal conditions, 

 and they can all be reproduced by chemical substances in solution 

 or in a particulate state. What constitutes their special feature 

 is their progressive or spreading nature, due to the bacterial 

 multiplication. 



(1) Local Lesions. In some diseases the lesion has a special 

 site ; for example, the lesion of typhoid fever and, to a less 

 extent, that of diphtheria. In other cases it depends entirely 

 upon the point of entrance, e.g. malignant pustule and the 

 conditions known as wound infections. In others again, there is 

 a special tendency for certain parts to be affected, as the upper 

 parts of the lungs in tubercle. In some cases the site has a 

 mechanical explanation. 



When organisms gain an entrance to the blood from a primary 

 lesion, the organs specially liable to be affected vary greatly in 

 different diseases. Pyogenic cocci show a special tendency to 

 settle in the capillaries of the kidneys and produce miliary 

 abscesses, whilst these lesions rarely occur in the spleen. On 

 the other hand, the nodules in disseminated tubercle or glanders 

 are much more numerous in the spleen than in the kidneys, 

 which in the latter disease are usually free from them. 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. Even in the case of the 

 lesions produced by dead tubercle bacilli, a certain selective 

 character is observed. 



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, and may be accompanied or 

 lead up to necrosis of the tissues of the part, a good example of 

 the latter event being found in a boil. Examples will be given 

 in subsequent chapters. The necrotic or degenerative changes 



