MODES OF ACTION. 225 



organism, or to exceptional pathogenic power acquired by some one 

 of the common bacteria which infest suppurating wounds, cannot be 

 determined in the absence of exact experiments by modern methods. 

 But the latter view has seemed to the writer the most probably cor- 

 rect. There are many facts which go to show that pathogenic viru- 

 lence may be increased by cultivation in animal fluids, and where 

 wounded men are brought together under unfavorable sanitary con- 

 ditions, as has been the case where hospital gangrene has made its 

 appearance, it may be that some common saprophyte acquires the 

 power of invading the exposed tissues instead of simply feeding upon 

 the secretions which bathe its surface. 



Koch has described a progressive tissue necrosis in mice, due to a 

 streptococcus, which he first obtained by inoculating a mouse in the 

 ear with putrid material. The morbid process is entirely local and 

 rapidly progressive, causing a fatal termination in about three days, 

 without invasion of the blood. 



In diphtheritic inflammations of mucous membranes we have 

 a local invasion of the tissues and a characteristic plastic exudation. 

 In true diphtheria the local inflammation and necrotic changes in 

 the invaded tissues are not sufficient to account for the serious gen- 

 eral symptoms, and we now have experimental evidence that the 

 diphtheria bacillus produces a very potent toxic substance to which 

 these symptoms are no doubt largely due. The diphtheria bacillus 

 of Loftier appears to be the cause of the fatal malady which goes 

 by this name, but undoubtedly other microorganisms may be con- 

 cerned in the formation of diphtheritic false membranes. In cer- 

 tain forms of diphtheria, and especially when it occurs as a com- 

 plication of scarlet fever, measles, and other diseases, the Klebs- 

 Loffler bacillus is absent, and a streptococcus, which appears to be 

 identical with Streptococcus pyogenes, is found in considerable num- 

 bers and is probably the cause of the diphtheritic inflammation. 

 An epidemic of diphtheria occurring among calves was studied by 

 Loffler, and is ascribed by him to his Bacillus diphtheria vitulo- 

 rum. The same bacteriologist has shown that the diphtheria of 

 chickens and of pigeons is due to a specific bacillus which differs 

 from that found in human diphtheria, and which he calls Bacillus 

 diphtherias columbrarum. 



Recently Prof. Welch has studied the histological lesions pro- 

 duced by filtered cultures of the diphtheria bacillus. Cultures in 

 glycerin-bouillon, several weeks old, were filtered through porce- 

 lain, and the sterile filtrate was injected beneath the skin of guinea- 

 pigs. One cubic centimetre of this filtrate was injected into a gui- 

 nea-pig on the 10th of December, and two cubic centimetres more on 

 the 14th of the same month. The animal succumbed at the end of 

 15 



