For example:  A farmer who is not conversant with any of these maladies, but who may have heard of the cow-pox in general terms, may acquaint a neighbouring surgeon that the distemper appears at his farm.  The surgeon, eager to make an experiment, takes away matter, inoculates, produces a sore, uneasiness in the axilla, and perhaps some affection of the system.  This is one way in which a fallacious idea of security both in the mind of the inoculater and the patient may arise; for a disease may thus have been propagated from a simple eruption only.

One of the first objects then of this pursuit, as I have observed, should be, to learn how to distinguish with accuracy between that peculiar pustule which is the true cow pock, and that which is spurious.  Until experience has determined this, we view our object through a mist.  Let us, for instance, suppose that the smallpox and the chicken-pox were at the same time to spread among the inhabitants of a country which had never been visited by either of these distempers, and where they were quite unknown before:  what confusion would arise!  The resemblance between the symptoms of the eruptive fever and between the pustules in either case would be so striking that a patient who had gone through the chicken-pox to any extent would feel equally easy with regard to his future security from the smallpox as the person who had actually passed through that disease.  Time and future observation would draw the line of distinction.

So I presume it will be with the cow-pox until it is more generally understood.  All cavilling, therefore, on the mere report of those who tell us they have had this distemper, and are afterwards found susceptible of the smallpox, should be suspended.  To illustrate this I beg leave to give the following history: 

Sarah Merlin, of the parish of Eastington in this county, when about thirteen or fourteen years of age lived as a servant with farmer Clarke, who kept a dairy consisting of about eighteen cows at Stonehouse, a neighbouring village.  The nipples and udders of three of the cows were extensively affected with large white blisters.  These cows the girl milked daily, and at the time she assisted, with two others, in milking the rest of the herd.  It soon appeared that the disease was communicated to the girl.  The rest of the cows escaped the infection, although they were milked several days after the three above specified, had these eruptions on the nipples and udders, and even after the girl’s hand became sore.  The two others who were engaged in milking, although they milked the cows indiscriminately, received no injury.  On the fingers of each of the girl’s hands there appeared several large white blisters—­she supposes about three or four on each finger.  The hands and arms inflamed and swelled, but no constitutional indisposition followed.  The sores were anointed with some domestic ointment and got well without ulcerating.