Contagious {Zymotic) Diseases. 3 



or their toxins unite with the constituents of such tissues so as 

 to abolish or derange their functions. The action may . be 

 likened to the election of aloes for the large intestines, jalap for 

 the small, saltpeter for the kidneys, opium or alcohol for the 

 brain. So the microbes of tetanus, dourine and rabies affect the 

 nervous system, those of aphthous fever the mouth, feet and 

 udder, those of glanders, tuberculosis and strangles the lymph 

 system, and those of cowpox the skin. 



Elimination of Pathogenic Microbes. 



Different microbes may leave the system by any of the natural 

 excreting surfaces. The mucosae of the bronchia, bowels, or 

 kidneys are the most usual outlets. The kidneys especially, re- 

 ceiving so much blood relatively to their^size, habitually pass out 

 microbes which find a home in the blood and thus the kidneys 

 are notoriously subject to secondary local infection and patho- 

 logic processes. 



Susceptibility : Vulnerability. 



Just as certain tissues are receptive of given microbian poisons 

 and succumb to them, so certain animals and species, suffer from 

 particular microbes and their products, when other tissues of the 

 same, or other species of closely allied animals, escape, The 

 latter are said to be immune, and this immunity is racial, or 

 innate on the one hand, or acquired on the other. The recog- 

 nized and assumed conditions of susceptibility will be more easily 

 dealt with under the head of immunity. 



Im,munity : Serum Therapy. 



Immunity may be defined as the successful resistance, by the 

 animal body, of invading microbes and their products. Con- 

 genital or racial immu7iity to given infections which prove patho- 

 genic to others is so common that a large number of infectious 

 diseases have been long recognized as peculiar to a given gAius 

 or species. Thus the horse has his strangles, influenza and con- 

 tagious pneumonia ; the ox his lung plague and Texas fever : 

 the sheep'\\.s sheep-pox caseous lymph adenitis and braxy ; th.&pig 

 its erysipelas (rothlauf ) and hog cholera ; the dog his distemper ; 



