l86 CLINICAL VP:TKRINAKV iMKDlCINK AND SUK(;ERV. 



we owe the histor}- of several carefull}' studied epidemics to certain of 

 our militar}- colleagues. 



Contagious pleuro-pneumonia of the horse results from the entrance 

 into and development within the organism of a specific pathogenic 

 microbe. Sometimes the animal is infected by contact with a diseased 

 subject, at others infection is mediate. The disease is most commonly 

 seen in large stables where the work necessitates frequent renewals of 

 stock. One of the new-comers is first affected ; a week to fourteen 

 days later a second shows s}'mptoms, and the disease successively 

 attacks a number of animals, comprising one third, one half, or two 

 thirds of the whole number, sometimes even more — in one of Cagnat's. 

 series tw^elve out of fifteen, and in some I have myself seen, seven out 

 of nine. 



The stables of horse dealers, omnibus companies, remount depots,, 

 cavalry quarters, and veterinary infirmaries, are most commonly 

 invaded. Once introduced the disease ma}- continue for a long time 

 in an enzootic form, diminishing and again re\iving, the revivals almost 

 always following the introduction of freshly bought horses. 



It attacks young, adult, and old animals, though certain ages are 

 more subject than others. Horses between four to eight years old, 

 especially if recently brought into work, are those most commonly 

 affected ; aged animals are less subject. If during an outbreak of this 

 form of pneumonia it becomes necessar}' to introduce fresh horses, aged 

 animals should always be gi\en the preference, 30ung horses almost 

 invariably becoming infected. 



In stables where the disease was raging I have often noticed that 

 horses which had previously suffered from an attack remained quite 

 unaffected. Many other practitioners have made the same observation. 

 An attack undoubtedly confers immunity for a certain period, some- 

 times during the animal's whole life ; though in most instances this 

 immunity diminishes and may entirel}' disappear with lapse of time. 

 Instances of recurrence, adduced in opposition to this idea, in no wise 

 weaken it, being readily explained by the man}- forms assumed by 

 pneumonia, and by the gradual loss of acquired immunity. 



Generally speaking, then, experience shows that one attack renders 

 the subject refractor}- or little susceptible to a second. Cagnat well 

 understood this, and with the courage of his con\-ictions even went so 

 far as to recommend that when purchasing preference should be given 

 to horses whose chtsts showed traces of the counter-irritants applied 

 during a previous attack of pneumonia. That is to say, he recom- 

 mended exactl}' the contrary of what is usuall}- practised. 



