MODES OF ACTION. 223 



genie power evidently depends, in some instances at least, upon these 

 toxic products of their growth, by which the vital resisting power of 

 the tissues is overcome. 



Among the bacteria which in this way produce extensive local 

 inflammatory and necrotic changes are certain anaerobic species 

 found in the soil and in putrefying material, such as the bacillus of 

 malignant oedema and the writer's Bacillus cadaveris. The bacillus 

 of symptomatic anthrax, an infectious disease of cattle, acts in the 

 same way. All of these produce toxic substances which have a very 

 pronounced local action upon the tissues invaded by them. Other 

 bacteria, while they develop chiefly in the vicinity of the point of 

 entrance by accident or by inoculation produce a potent toxic sub- 

 stance which gives rise to general symptoms of a serious character, 

 such as tetanic convulsions (bacillus of tetanus) or intense fever and 

 nervous phenomena (micrococcus of erysipelas). Again, the local 

 irritation resulting from the presence of parasitic bacteria may pri- 

 marily give rise to the formation of new growths having a low grade 

 of vitality, which later may undergo necrotic changes, as in tubercu- 

 losis, glanders, and leprosy. In this case constitutional symptoms 

 are not present, or are of a mild character during the development 

 of these new formations, which apparently result from the local ac- 

 tion of substances eliminated during the growth of the parasite, 

 rather than from its simple presence. This is an inference based 

 upon the fact that non-living particles, or even living parasites, as in 

 trichinosis, do not produce similar new growths composed of cells, 

 but become encysted in a fibrous capsule. 



In pneumonia we have a local process in which one or more lobes 

 of the lung are invaded by a pathogenic micrococcus (Micrococcus 

 pneumonise crouposoe) which induces a fibrinous exudation that com- 

 pletely fills the air cells. How far the symptoms of the disease are 

 due to the local inflammation and disturbance of function, and to 

 what extent they may be due to the absorption of a soluble toxic 

 substance evolved as a result of the growth of the micrococcus, has 

 not been determined. But the mild character of the general symp- 

 toms when a limited area of lung tissue is involved leads to the in- 

 ference that the pathogenic power of this particular pathogenic 

 microorganism is chiefly exercised locally. 



The pus cocci and various other saprophytic bacteria, when intro- 

 duced beneath the skin, give rise to the formation of abscesses, un- 

 attended by any very considerable general disturbance ; and also to 

 secondary purulent accumulations metastatic abscesses. 



That this is not due simply to their mechanical presence is shown 

 by the fact that powdered glass and other inert substances, when 

 thoroughly sterilized, do not give rise to pus formation when intro- 



