158 RELATIONS OF BACTERIA TO DISEASE 



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 

 vascular phenomena. It may here be pointed out that a well- 

 marked 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 

 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 the human subject, the 

 lesion 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, bnt on the other hand, this is often impossible. These 

 changes often include the occurrence of degenerations or of 

 actual necrosis in the newly formed tissue. In the granulomata, 

 infection of other parts from the primary lesion takes place 

 chiefly by the blood vessels and lymphatics, though sometimes 

 along natural tubes such a& the bronchi, intestine, etc. 



(2) General Lesions produced by Toxins. In the various in- 

 fective conditions produced by bacteria, changes commonly 

 occur in certain organs unassociated with the presence of the 

 bacteria; these are produced by the action of bacterial pro- 

 ducts circulating in the blood. Many such lesions can be pro- 

 duced experimentally. The secreting cells of various organs, 

 especially the kidney and liver, are specially liable to change 

 of this kind. Cloudy swelling, which may be followed by fatty 

 change or by actual necrosis with granular disintegration, is 



