VETERINARY MEDICINE. 



CONTAGIOUS (ZYMOTIC) DISEASES. 



Contagious or Infectious Diseases are such as are transferred 

 from animal to animal by an infinitesimal microbe or a parasite, 

 which propagates itself in or on the body of the victim. This 

 volume is devoted to the microbian diseases in which the essen- 

 tial cause is an infinitesimal microscopic organism introduced 

 from without and propagating itself in the body as similar or- 

 ganisms do in fermenting liquids or solids. The parallel with 

 fermentation has given rise to the Greek name zymotic. As 

 there can be no fermentation without the living organized fer- 

 ment, so there can be no zymotic disease without the pathogenic 

 microbe. The pathogenic microbes are divided into those belong- 

 ing to the vegetable kingdom — bacteria, and those, belonging to 

 the animal — protozoa. All however pertain to the very lowest 

 forms of their respective kingdoms, nearing the line on which 

 the two kingdoms meet. 



The microbes establish their pathogenic action in a variety of 

 ways of which one or two examples may be named. Some, like 

 the bacillus anthracis are so avid of oxygen that they rob the 

 blood of that essential element and unfit it for the functions of 

 life. Some like the trypanosoma, or the pyroplasma bigeminum 

 liquefy and destroy the red globules of the blood, quickly re- 

 ducing it to a dilute condition unfit for its normal uses. Some 

 like bacillus tetani produce toxins which unite with body tissues 

 or cells or their constituents, and cause disorder or loss of their 

 normal functions and consequent disease. 



Infection Atria. 



Pathogenic germs may enter the system through the mucous 

 membrane of the air-passages, eyes, alimentary canal, urino- 

 generative organs, mammary glands, etc., and especially through 

 the glandular structures in such membranes, or opening through 

 them. The follicles of the tonsils, solitary and agminated glands 



