136 CONTAGION AND CONTAGIOUS DISEASES. 



in a few hours after inoculation, whilst the deleterious effects of 

 the pleuro-pneumonia contagium, or that of rabies, may not be 

 developed for weeks or even months after introduction into the 

 body. Some contagious poisons again seem to affect one class 

 of animals : thus pleuro-pneumonia is peculiar to horned cattle ; 

 epizootic eczema originates in cattle and sheep, but is capable 

 of transmission by direct contact to many other animals, and 

 even to man ; glanders affects the horse and ass, but is com- 

 municable to man, dogs, sheep, goats, rabbits, and mice by 

 inoculation ; and rabies, originating in the dog, is capable of 

 transmission to the majority of animals and to man by inocula- 

 tion. These peculiarities in the action of morbid poisons are 

 mysterious and unaccountable. We must, however, accept them 

 as facts that investigation may some day throw light upon. 



Contagious diseases, whether induced by obligatory or by 

 facultative parasites, may assume an enzootic, epizootic, or even 

 panzootic character, the great feature of which is a tendency to 

 spread rapidly, attacking large numbers of animals in a short 

 space of time, destroying many and incapacitating a large 

 majority. 



The term epizootic is derived from the Greek, Eiri, upon, and 

 Swoi/, an animal. Diseases of this order are said to arise from 

 enzootic influences — from Ev, in, and Swof, an animal. Enzootic 

 influences are those peculiar to certain districts, and result from 

 conditions or agencies peculiar to a locality, which favour the 

 development of various miasmatic diseases, such influences be- 

 coming epizootic, or affecting the many, from causes as yet 

 unknown. In this order of diseases may be included the 

 catarrhal fever or influenza which prevails more or less at all 

 times amongst the horses of large cities and certain localities. 

 Such diseases may be said to dwell in certain localities, having, 

 however, the tendency to spread rapidly. They are then said 

 to be epizootic, or even panzootic. 



