632 VETEEINAEY HYGIENE 



INFECTIOUS DISEASES COMMON TO ANIMALS AND MAN. 



The study of hygiene was stimulated by, in fact based 

 upon, a desire to unravel the mystery which so often sur- 

 rounds outbreaks of infectious disease. As education became 

 more general, science was no longer satisfied with the 

 explanation that disease was due to an act of God, but that 

 there must be certain definite conditions existing which 

 only required looking for. 



A search for these led to a study of air, food, water, soils, 

 drainage, etc. ; in fact, no necessary conditions or surround- 

 ings of life have been neglected to throw light upon the all- 

 important problem of how disease is produced. Unfortu- 

 nately, this has not always been attended by satisfactory 

 results ; that disease can be traced to defective surroundings 

 and local conditions we have had an opportunity for see- 

 ing, but that the particular class discussed in the present 

 chapter could originate in this way was long disputed, and 

 the argument finally crushed by the proof, so easy of 

 demonstration, that the spontaneous origin of living matter 

 is an impossibility. 



We have seen that a study of the laws of health helped 

 to account for the outbreak and spread of infectious disease, 

 but did not go far enough ; everything was reduced to con- 

 jecture until the new science of bacteriology revealed an 

 unknown world to our senses, and explained with precision, 

 and by the simplest methods, what was previously utter 

 darkness. 



It was Pasteur's work which gave the death blow to the 

 spontaneous origin of infectious diseases ; the youthful 

 science of bacteriology has, ever since that time, gone on 

 year by year unravelling the mystery surrounding infection, 

 with the most astonishing and often unexpected results. 



There are some infectious diseases peculiar to certain 

 animals ; for example, strangles only affects the horse ; 

 cattle plague and pleuro-pneumonia, the ox ; swine fever, 

 the pig ; sheep-pox, braxy, and louping-ill, the sheep ; dis- 

 temper, the dog ; scarlet fever, diphtheria, and typhoid 



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