LOCAL LESIONS 189 



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 con- 

 ditions 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 accom- 

 panied by abundant fibrinous exudation, or by great catarrh (in 

 the case of an epithelial surface), or by haemorrhage, or by 

 cedema ; it may be localised or spreading in character ; it may 

 be followed by suppuration, and may 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 affecting 

 especially the more highly developed elements of tissues are 

 chiefly produced by the direct action of the bacterial poisons, 

 though aided by the disturbances of nutrition involved in the 



