VARIOLA EQUINA. 489 



in the human family, but is comparatively simple. It is 

 an acute febrile disease, producing erui)tions or pustules, 

 and, like all febrile diseases, runs a certain course. It 

 belongs to the zymotic class of diseases, and is propagated 

 solely by contagion, so far as our present state of know- 

 ledge goes. After exposure and contagion there is the 

 usual period of incubation, followed by fever, and, in due 

 course of time, an eruption, which appears in the form of 

 small reddish nodules, each, in size, somewhat smaller than 

 a pin's-head, and surrounded by a red areola. These 

 nodules gradually change in character and become vesicles, 

 containing a clear lymph, which in due course of time 

 loses its transparency and becomes purulent. The pustules 

 burst, and discharge their contents, forming a dry crust or 

 scales, which ^vear off in a few days. There is a primary 

 fever and a secondary fever. The fever in a majority of 

 cases is most severe just before the eruption. The disease 

 is usually of a benign character. 



Sijmptoms. — The symptoms of variola, as it occurs in the 

 horse, are dulness, more or less fever — in many cases 

 being so slight as to almost escape notice ; the pulse be- 

 comes somewhat quickened and weaker than usual ; there is 

 increased thirst, and the appetite becomes impaired. Soon 

 red patches appear upon the skin, and these patches are 

 depressed in the centre. The nodules appear most thickly 

 about the mouth, nose, Schneiderian membrane, heels, etc , 

 and gradually taking on the character of vesicles, become filled 

 with transparent lymph. The pustular stage now follows, 

 the vesicles becoming pustules, which break and discharge, 

 in some cases, several times in succession. These pustules 

 may become confluent, and when running together on the 

 pituitary membrane have caused the disease to be mistaken 

 for glanders. When the mouth is much affected the animal 

 masticates with difficulty. Variola runs its course in from 



