150 RELATIONS OF BACTERIA TO DISEASE. 



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, ery- 

 sipelas, 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-marked inflammatory re- 

 action 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 

 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 diseases often known as the infective granulomata, of 

 which tubercle, leprosy, glanders, actinomycosis, syphilis, 

 etc., are examples. A hard and fast line, however, cannot 

 be drawn between such conditions and those described 

 above as acute. In glanders, for example, especially in 

 man, the lesion produced by the glanders bacillus often 

 approaches very nearly to an acute suppurative change, 

 and sometimes actually is of this nature. Whilst in these 

 diseases the fundamental change is the same, viz., a re- 

 action to an irritant of minor intensity, the exact 

 structural characters and arrangement vary in different 

 diseases. In some cases the disease may be identified by 

 the histological changes alone, but on the other hand, 

 this is often impossible. In tubercle, for example, in 

 addition to the proliferative change, a cellular necrosis 



