DISEASES OF THE OX AND SHEEP. 309 



and to the human being an affection exactly like that brought 

 on by ordinary vaccination. It seems highly probable that cow- 

 pox is nothing else than small-pox communicated to the cow from 

 man, and thereby deprived of its virulence. In support of this 

 view, the fact that cow-pox, when inoculated from cow to cow, 

 tends before long to die out, presents itself for consideration. 



Vaccination. 



When the material of cow-pox is inoculated on a human 

 being, about the end of the second day or the beginning of the 

 third day a small congested papule appears. This papule 

 gradually increases in size, and about the fifth day becomes a 

 circular greyish vesicle, with a depressed centre. About the 

 eightli day it is Inrgest, has a cupped surface, and contains a 

 colourless and transparent viscid fluid, which about this time 

 begins to become purulent. A red areola forms, and some 

 thickening of the inflamed area occurs, and increases until the 

 tenth day. The areola also attains a diameter of about two 

 inches. At the close of about ten and a half days the pustule 

 begins to dry up, and the areola and other signs of inflammation 

 to subside. At about fourteen and a half days from the outset, 

 a hard and dark-coloured scab has formed. This blackens, and 

 at about twenty-two and a half days from the beginning falls 

 off, leaving a depressed, pitted, permanent scar. 



In association with these local changes, there is also manifested 

 a rise of temperature, even sometimes on the fourth day ; and 

 at a later time, for instance, from the eighth to the tenth or 

 eleventh day, together with the development of the areola, 

 the temperature rises still higher, and there is much restlessness, 

 and loss of appetite. The glands above the seat of the operation 

 are enlarged and painful, and sometimes a roseolous rash spreads 

 over the vaccinated limb, and perhaps to other parts. This 

 rash may be vesicular or papular. The consequences of vacci- 

 nation direct from the cow are identical with those resulting 

 from vaccination with humanised lymph. If a person is re- 

 vaccinated, there may be merely a little local irritation or a 

 development of the typical pock. The papule may attain its 

 full development about five and a half days after the operation, 

 and very soon afterwards form a scab, which falls off in the 

 course of a day or two. 



