. 
474 VARIOLA—POX IN ANIMALS 
15. Torrey anp Raue., Studies in canine distemper. Jour. Med. Research, 
Vol. XXVII (1913), p. 291. 
16. Youart. On vaccination of the dog. Proc. of the Vet. Med. Asso., 1837, p. 
60. (Quoted by Gray.) 
VARIOLA—POX IN ANIMALS 
General consideration. Variola is an acute infectious exanthema- 
tous disease affecting man and a number of species of domesticated 
animals. Variola is used generically, when applied to the disease of 
lower animals, as the identity of the virus causing the disease in the 
different species is not positively determined. In man it refers to 
small pox. Variola presents in old animals a characteristic vesicular, 
pustular eruption which develops on the skin over the entire body or 
only over certain parts. In the beginning there is a rise of tempera- 
ture followed by the eruptions peculiar to the disease. 
The papular stage. This commences with the appearance of small 
red spots resembling flea-bites. These, by proliferation of cells into 
the papillary layer and rete mucosum, are formed into small papules 
or firm nodules. 
The vesicular stage. In this the proliferation of cells increases. 
They collect in clusters or groups, separated from each other by septa 
or walls formed chiefly by the epidermic cells. Exudation next takes 
place, and the lymph collects in these spaces. The vesicle thus differs 
from that produced by an ordinary vesicant, in which there is but a 
single sac formed. The summit of the vesicle becomes clear, and in 
that of cow-pox there is a slight depression or umbilication in the 
centre. During the next stage, that of suppuration, the septa break 
down and the umbilication disappears. 
The pustular stage. In this the vesicle becomes a pustule, its con- 
tents turbid and purulent, and its summit assumes a globular form 
and a greyish-yellow color. An areola of congestion occurs around 
the pustules, and the skin between them becomes swollen. 
The stage of desiccation. In this the pustule dries up, at first in the 
form of yellowish scales, which later on become a dark brown crust. 
Desquamation occurs, and a white shining cicatrix or a brownish-red 
spot may be left, which is known as a “pit.” This results from 
destruction of the superficial layer of the dermis. 
In the development of the tissue changes peculiar to the maturity 
of the lesions we have the result of the action of the virus itself while 
the subsequent suppuration of the contents of the vesicles is produced 
by pyogenic micrococci and streptococci. 
