VAETOLA VACCINA. 207 



knowledge that, tliroiigli the keen penetration of Jenner, the 

 disease directly communicated by vaccination from the lower 

 to the higher animal has proved a blessing to millions of the 

 human race. 



There are many forms of eruption in the udder of the cow, 

 which are sometimes confounded with those of variola; but those 

 of variola have certain characteristics which distinguish them 

 from all other, or so-called spurious, forms of the disease. The 

 local symptoms of the true variola are heat, swelling, and 

 tenderness of the teats for three or four days, followed by 

 irregular pimply hardness of the skin, more particularly about 

 the base of the teats. The pimples may sometimes be felt in 

 five days after communication ; they assume a red hue when 

 about the size of a pea, are very painful and hard, gradually 

 increase in size, and in other three or four days attain that of a 

 horse-bean, assuming a circular form on the udder, and an oblong 

 on the teats. They rise in the centre, become more or less 

 pointed (acuminated), containing at first a clear, and ultimately 

 a turbid fluid. If the vesicles are broken, troublesome sores 

 supervene, the discharge from Avhich will communicate the 

 disease to the milker, if he is not already protected by previous 

 vaccination. The vesicles, if not broken, become depressed in 

 their centres, and have an indurated margin, around the circum- 

 ference of which the skin denotes active inflammation by a circle 

 of redness, acquiring their maximum size about the tenth day, 

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

 black solid scabs or crusts form upon the surfaces. Some of 

 these scabs may be seen semi-detached, others entirely so, ex- 

 posing a raw surface, with a slight central slough. Vesicles, 

 pustules, and scabs may be witnessed on the same teat at one 

 and the same time, indicating the formation of new crops of 

 vesicles at different periods. The crusts, if left undisturbed, 

 gradually become thicker, darker, and more compact until about 

 the fourteenth day, and spontaneously separate about the end of 

 three weeks, leaving shallow, smooth, oval, or circular pits of a 

 pale rose colour, with some traces of surrounding induration. 



The depression in the pocks is accounted for in various ways. 

 Dr. Petzholdt thinks it is caused by the ducts of the cutaneous 

 glands, which are ruptured as the pustules fill with pus and 

 maturate, but which, in the early period of the eruption, Ijind 



