BACTERIA IN INFECTIOUS DISEASES. 257 



and antiseptic treatment. Its progress cannot, 

 however, be arrested by ordinary antiseptic appli- 

 cations ; for the pathogenic organism (hypothetical 

 as yet) invades the tissues to a certain depth, and 

 its destruction requires something more than a 

 superficial germicide action, e. g., bromine, nitric 

 acid, the hot iron. 



Diphtheria, also, is a disease in which there seems 

 to be good reason for believing that the different 

 degrees of virulence are due to circumstances re- 

 lating to the genealogy of the infecting organism, 

 as well as to the resisting power of the infected 

 individual ; and that, as in anthrax and in fowl- 

 cholera, physiological varieties of the pathogenic 

 micrococcus, to which this disease is probably due, 

 may be developed by special conditions relating to 

 its environment, either in the fauces of an infected 

 individual or external to the human body. 



It is not alone by invading the blood or tissues 

 that bacteria exhibit pathogenic power. Chemical 

 products evolved during their vital activity, ex- 

 ternal to the body, or in abscesses and suppurating 

 wounds, or in the alimentary canal, may doubtless 

 be absorbed and exercise an injurious effect upon 

 the animal economy. Indeed, we have experi- 

 mental evidence that most potent poisons are pro- 

 duced during the putrefactive decomposition of 

 organic matter. The poisons, resembling the vege- 

 table alkaloids in their reactions, called ptomaines 

 by Selmi, who first obtained them from a cadaver, 

 are fatal to animals in extremely minute doses. 



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