LOCAL LESIONS. 167 



may be followed by suppuration, or may lead to necrosis. A 

 few examples may be given. A great many different organ- 

 isms cause an abundant fibrinous exudation. This, along with 

 necrosis of epithelium, is the action of the diphtheria bacillus on 

 a mucous membrane, and also of streptococci in certain condi- 

 tions ; it is produced in the alveoli of the lung in croupous pneu- 

 monia by the pneumococcus and probably by other organisms, 

 whilst fibrinous inflammation in serous cavities is produced by a 

 great many different bacteria. The last statement also applies 

 to numerous suppurative and catarrhal conditions. The in- 

 flammatory change in a Peyer's patch in typhoid fever, though 

 fibrinous exudation is less marked, is followed by necrosis, while 

 in the malignant pustule of man necrotic change attended by 

 considerable haemorrhage is one of the chief features. The 

 great variety in local reaction is well illustrated in the case of 

 skin lesions produced by bacteria. The necrotic or degenerative 

 changes affecting especially the more highly developed elements 

 are chiefly produced by the direct action of the bacterial poisons, 

 though aided by the disturbances of nutrition involved in the 

 vascular phenomena. 



In many of the acute inflammatory conditions, if not attended 

 by a fatal result, the disease comes to a natural termination after 

 a certain time, e.g. in pneumonia, erysipelas, etc. This fact, 

 the explanation of which is not yet fully understood, has an 

 important relation to the subject of immunity, and will be 

 discussed later. It may also be pointed out that a well-niarked 

 inflammatory reaction is often found in animals which occupy 

 a medium position in the scale of susceptibility, and that an 

 organism which causes a general infection in a certain animal 

 may produce only a local inflammation when its virulence is 

 lessened. 



Chronic Local Lesions. In a considerable number of diseases 

 produced by bacteria the local tissue reaction is a more chronic 

 process than those described. In other words, the specific 

 irritant is less intense, so that there is less vascular disturbance 

 and a greater preponderance of the proliferative processes, 

 leading to new formation of connective tissue or a modified 

 connective tissue. This formation may occur in foci here and 

 there, so that nodules of greater or less consistence result, or it 

 may be more diffuse. Such changes especially occur in the 



