184 EDWARD JENNER 



certainly requires some attention in discriminating it. The 

 most perfect criterion by which the judgment may be guided 

 is perhaps that adopted by those who attend infected cattle. 

 These white blisters on the nipples, they say, never eat into 

 the fleshy parts like those which are commonly of a bluish 

 cast, and which constitute the true cow-pox, but that they 

 affect the skin only, quickly end in scabs, and are not nearly 

 so infectious. 



That which appeared to me as one cause of spurious erup- 

 tions, I have already remarked in the former treatise, name- 

 ly, the transition that the cow makes in the spring from a 

 poor to a nutritious diet, and from the udder's becoming at 

 this time more vascular than usual for the supply of milk. 

 But there is another source of inflammation and pustules 

 which I believe is not uncommon in all the dairy counties in 

 the west of England. A cow intended to be exposed for sale, 

 having naturally a small udder, is previously for a day or 

 two neither milked artificially nor is her calf suffered to have 

 access to her. Thus the milk is preternaturally accumulated, 

 and the udder and nipples become greatly distended. The 

 consequences frequently are inflammation and eruptions 

 which maturate. 



Whether a disease generated in this way has the power of 

 affecting the constitution in any peculiar manner I cannot 

 presume positively to determine. It has been conjectured to 

 have been a cause of the true cow-pox, though my inquiries * 

 have not led me to adopt this supposition in any one in- 

 stance ; on the contrary, I have known the milkers affected 

 by it, but always found that an affection thus induced left the 

 system as susceptible of the smallpox as before. 



\Yhat is advanced in my second position I consider also of 

 very great importance, and I could wish it to be strongly im- 

 pressed on the minds of all who may be disposed to conclude 

 nastily on my observations, whether engaged in their inves- 

 tigation by experiments or not. To place this in its clearest 

 point of view (as the similarity between the action of the 

 smallpox and the cow-pox matter is so obvious) it will be 

 necessary to consider what we sometimes observe to take 

 place in inoculation for the smallpox when imperfect vario- 

 lous matter is made use of. The concise history on this sub- 





