224 MODES OF ACTION. 
duced beneath the skin or injected into the cavity of the abdomen. 
On the other hand, it has been demonstrated by the experiments of 
Grawitz, De Bary, and others that certain chemical substances 
which act as local irritants when brought in contact with the tissues 
may induce pus formation quite independently of microérganisms : 
nitrate of silver, oil of turpentine, and strong liquor ammonie have 
been shown to possess this power. And it has been demonstrated by 
the recent experiments of Buchner that sterilized cultures of a long 
list of different bacteria—seventeen species tested—give rise to sup- 
puration when introduced into the subcutaneous tissues. 
Buchner has further shown that this property of inducing pus for- 
mation resides in the dead bacterial cells and not in soluble products 
present in the cultures. For, the clear fluid obtained by passing 
these sterilized cultures through a porcelain filter gave a negative re- 
sult, while the bacteria retained by the filter, although no longer 
capable of development, having been killed by heat, invariably 
caused suppuration. 
Individuals suffering from malnutrition are more susceptible to 
invasion by specific disease germs or by the common pus cocci 
than are those in vigorous health. Thus the sufferers from starva- 
tion, from crowd poisoning, sewer-gas poisoning, etc., are not only 
liable to be early victims during the prevalence of an epidemic dis- 
ease, but are very subject to abscesses, boils, ulcers, etc. A slight 
abrasion in such an individual, inoculated by the ever-present pus 
cocci, may give rise to an obstinate ulcer or a phlegmonous inflam- 
mation. 
In the same way some of the ordinary saprophytes, which usually 
have no pathogenic power, may be pathogenic for an animal whose 
strength is reduced by disease or injury. Thus necrotic changes 
may occur in injured tissues, or in those which havea deficient blood 
supply—from occlusion of an artery, for example—due to the presence 
of putrefactive bacteria which are incapable of development in the 
circulation of a healthy animal or in healthy tissues. We may also 
have a progressive gangrene, due to infection of wounds by bacteria 
which are able to invade healthy tissues. This is seen in the so- 
called hospital gangrene, which is undoubtedly due to microérgan- 
isms, although the species concerned in its production has not been 
determined, owing to the fact that modern bacteriologists have had 
few, if any, opportunities for studying it. The history of the disease, 
its rapid extension in infected surgical wards, the extensive slough- 
ing which occurs within a few hours in previously healthy wounds, 
and the effect of deep cauterization by the hotiron, nitric acid, or 
bromine in arresting the progress of the disease, all support this view 
of its etiology. Whether itis due toa specific pathogenic micro- 
