334 Veterinary Medicine. 



animals. The first indication of the lesion is the appearance on 

 the skin of fine points of congestion like fleabites. This is fol- 

 lowed by active diapedesis and proliferation of cells in the papil- 

 lary layer and rete mucosum, constituting the nodule or pimple 

 stage. In smallpox this is so firm and definitely outlined that it 

 has been compared to the presence of a shot in the skin. As the 

 proliferation of cells increases these form in separate clusters or 

 groups, isolated from each other by septa or walls largely made 

 up of the epidermic cells. In the next stage, therefore, when 

 exudation takes place the lymph accumulates in the spaces occu- 

 pied by the clusters of growing cells, and is found in a series 

 of chambers more or less perfectly separated from each other, so 

 that to evacuate the whole vesicle, each minute sac must be punc- 

 tured independently. The vesicles thus differ from others caused 

 by ordinary irritants in that each is chambered, instead of form- 

 ing one common undivided sac, which may be emptied by a single 

 puncture. In the next stage, when suppuration ensues, the septa 

 usually undergo liquefaction, so that the liquid occupies one 

 individed cavity in each pustule. For this reason the cen- 

 tral depression seen in the larger vesicles (cowpox) in their early 

 stage tends to disappear in the pustule. It may reappear later in 

 the resulting scab. Desiccation, scabbing and desquamation com- 

 plete the course of the affection, a distinct pit being left as a 

 result of the destruction of the superficial layer of the dermis. 



Nomenclature. The term variola is believed to come from the 

 lyatin varius (variegated, spotted) and pox from the Saxon pock 

 (pouch). The specific names, drawn from these tongues sus- 

 tain this view: As, variola vaccina, cow-pox, kine-pox ; variola 

 equincB, horse-pox; variola ovina, sheep-pox; variola caprina, 

 goat-pox; variola suillce, swine-pox; variola canina, dog-pox. 

 Tlie term smallpox, (^petite verole') is deduced from the small size 

 of the vesicle as compared with that of cow-pox, just as the 

 same has originated the term smallpox in sheep. 



History. Variola has undoubtedly existed from very ancient 

 times. Moore found it referred to in Chinese records of 1122 

 years before Christ, but it was only clearly described early in the 

 tenth century by Rliazes an Arabian physician. Gregory, how- 

 ever, found the name variola in I<atin manuscripts in the British 

 Museum of a much earlier date. The early epidemics of small 



