MODES OF ACTION. 223 
genic 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 anaérobic species 
found in the soil and in putrefying material, such as the bacillus of 
malignant cedema 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 alow 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 
pheumoniz croupos) 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 
microérganism 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- 
