Etiology : Causes of Disease. 1 3 



in a distillery stable usually ruin cattle for stock purposes. 

 Over exertion on the other hand is prolific of illness. Exhaustion 

 of the muscles, congestion, inflammation, cramps, congested 

 lungs, heart failure or rupture, apoplexies and other haemor- 

 rhages are among the resultant maladies. Auto-poisoning is an- 

 other result shown in equine haemoglobinaemia, and the fever of 

 leucomaines. The excessive development of sarcolactic acid from 

 muscular work may render an insusceptible animal susceptible to 

 the anthrax bacillus. Mechanical causes would include overexer- 

 tion, in the production of strains, fractures, and other injuries. 

 They would also include impaction by foreign bodies, calculi, and 

 ingesta, friction of folds of skin or by harness and other objects, 

 and pressure which leads to absorption and atrophy. To these 

 must be added poisons of vegetable, mineral and animal origin 

 and the microorganisms which act as injurious ferments within 

 the animal body. These will be treated more fully later on. Of 

 the microorganisms it may be said here, that they are almost cer- 

 tainly the cause of all transmissible diseases. These diseases are 

 variously named on the basis of different ideas. They are 

 enthetic, that is implanted as a seed is planted in the ground to 

 grow and multiply. They are zymotic or fermentative because 

 the essential cause multiplies and is propagated like a ferment. 

 They are contagious because propagated by contact mediate or 

 immediate. They are infectious when transmitted, not alone 

 by contact but through the atmosphere. They are epizootic be- 

 cause they tend to attack animals generally or a given genus or 

 family of animals generally when these are exposed to the infec- 

 tion. They are enzootic when confined to the animals in a given 

 locality, the soil or conditions of which are favorable to the pres- 

 ervation of the germ in pathogenic potency, or to the production 

 of a special susceptibility in the animal system. They are 

 sporadic when each case occurs without any causal relation to 

 another. They are called panzootic when they attack all ani- 

 mals without apparent preference. The term panzootic is also 

 used to describe those recrudescences of a disease or cycles of 

 exalted pathogenesis which are observed in contagious diseases, 

 which frequently last for years and again give place to a period 

 of benignancy. Such cycles, of malignancy and benignancy, 

 may be due to modified environment acting either on the disease- 

 germ or the animal system, or on both simultaneously. 



