CONTAGIOUS DISEASES OF CATTLE. 445 



VARIOLA VACCINAE (Cow-Pox). 



This disease is seen in most parts of the glo'be, and is not at- 

 tended with any great fatality. It is a contagious, febrile, and 

 eruptive disease, resulting from the presence of a specific virus 

 in the body. The period of incubation is from six to nine days. 

 The disease causes eruptions, principally upon the mammary 

 gland. The disease runs a definite and mild course, and destroys 

 the susceptibility of the affected animal to another attack. The 

 origin of the disease is not known. Jenner believed that cow- 

 pox and small-pox had their common origin in the ''grease" of the 

 horse. AVhether man had the disease communicated to him from 

 the lower animals, or whether horses and cows had it from man 

 is not determined. The origin will perhaps forever remain a 

 mystery. But let that be as it may, the disease, through the 

 experiments of Jenner, who directly communicated it by vacci- 

 nation from the lower to the higher animals, has proved a bless- 

 ing to millions of the human race. The local symptoms of true 

 variola are heat, swelling, and tenderness of the teats for three 

 or four days, followed by irregular pimples, more particularly 

 about the base of the teats. When the pimples are about the 

 size of a ])ea they assume a red hue. They gradually increase in 

 size, are painful and hard, becoming circular in form on the 

 udder and oblong on the teats. Finally, they rise in the center, 

 become pointed, and contain at first a clear, and ultimately a tur- 

 bid, fluid. They reach their maximum size about the tenth day, 

 and are then pustular; as the pustules dry, dark brown or black 

 solid scabs or crusts form upon the surface. Vesicles, pustules, 

 and scabs may be seen on the teat at any time. The crusts, if left 

 undisturbed, gradually become thicker and darker, until about 

 the fourteenth day; at the end of three weeks they spontaneously 

 separate, leaving shallow, smooth, oval, or circular pits of a pale 

 rose color, with some traces of surrounding induration. If the 

 vesicles are broken during their progress, troublesome sores su- 

 pervene, the discharge from which will communicate thie disease 



