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 microorganisms : 

 nitrate of silver, oil of turpentine, and strong liquor ammonise 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 have a 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 microorgan- 

 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 hot iron, nitric acid, or 

 bromine in arresting the progress of the disease, all support this view 

 of its etiology. Whether it is due to a specific pathogenic micro- 



