184 RELATIONS OF BACTERIA TO DISEASE 



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 ; there is less vascular disturbance 

 and a greater preponderance of the proliferative processes, lead- 

 ing to new formation of connective tissue. This formation 

 may occur in foci here and there, so that nodules 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 namely, a reaction 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. 



(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 products 

 circulating in the blood. Many such lesions can be produced 

 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 common. 

 Hyaline change in the walls of arterioles may occur, and in 

 certain chronic conditions amyloid change is brought about in 

 a similar manner. The latter has been produced in animals 

 by repeated injections of the staphylococcus aureus. Capillary 

 haemorrhages are not uncommon, and are in many cases due to 

 an increased permeability of the vessel walls, aided by changes 

 in the blood plasma, as evidenced sometimes by diminished 

 coagulability. Similar haemorrhages may follow the injection of 

 some bacterial toxins, e.g. of diphtheria, and also of vegetable 

 poisons, e.g. ricin and abrin. Skin eruptions occurring in the 

 exanthemata are probably produced in the same way, though in 



