A HISTORY OF SCIENCE 



of domestication, is frequently subject," wrote Jenner, 

 in his famous paper on vaccination. "The farriers 

 call it the grease. It is an inflammation and swelling 

 in the heel, accompanied at its commencement with 

 small cracks or fissures, from which issues a limpid 

 fluid possessing properties of a very peculiar kind. 

 This fluid seems capable of generating a disease in the 

 human body (after it has undergone the modification 

 I shall presently speak of) which bears so strong a 

 resemblance to small-pox that I think it highly prob- 

 able it may be the source of that disease. 



" In this dairy country a great number of cows are 

 kept, and the office of milking is performed indiscrim- 

 inately by men and maid servants. One of the former 

 having been appointed to apply dressings to the heels 

 of a horse affected with the malady I have mentioned, 

 and not paying due attention to cleanliness, incau- 

 tiously bears his part in milking the cows with some 

 particles of the infectious matter adhering to his fin- 

 gers. When this is the case it frequently happens that 

 a disease is communicated to the cows, and from the 

 cows to the dairy-maids, which spreads through the 

 farm until most of the cattle and domestics feel its un- 

 pleasant consequences. This disease has obtained the 

 name of Cow-Pox. It appears on the nipples of the 

 cows in the form of irregular pustules. At their first 

 appearance they are commonly of a palish blue, or 

 rather of a color somewhat approaching to livid, and 

 are surrounded by an inflammation. These pustules, 

 unless a timely remedy be applied, frequently degen- 

 erate into phagedenic ulcers, which prove extremely 

 troublesome. The animals become indisposed, and 



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