The application of the ointment with the hydr. nit. rub. was made use of for three days, when, the state of the pustule remaining stationary, it was exchanged for the ung. hydr. nit. This appeared to have a more active effect than the former, and in two or three days the virus seemed to be subdued, when a simple dressing was made use of; but the sore again shewing a disposition to inflame, the ung. hydr. nit. was again applied, and soon answered the intended purpose effectually. The girl, after the tenth day, when, as has been observed, she became a little ill, shewed not the least symptom of indisposition. She was afterwards exposed to the action of variolous; matter, and completely resisted it. Susan Phipps also went through a similar trial. Conceiving these cases to be important, I have given them in detail: first, to urge the precaution of using such means as may stop the progress of the pustule; and, secondly, to point out (what appears to be the fact) that the most material indisposition, or at least that which is felt most sensibly, DOES NOT ARISE PRIMARILY FROM THE FIRST ACTION OF THE VIRUS ON THE CONSTITUTION, BUT THAT IT OFTEN COMES ON, IF THE PUSTULE IS LEFT TO CHANCE, AS A SECONDARY DISEASE. This leads me to conjecture, what experiment must finally determine, that they who have had the smallpox are not afterwards susceptible of the primary action of the cow-pox virus; for seeing that the simple virus itself, when it has not passed beyond the boundary of a vesicle, excites in the system so little commotion, is it not probable the trifling illness, thus induced may be lost in that which so quickly, and oftentimes so severely, follows in the casual cow- pox from the presence of corroding ulcers? This consideration induces me to suppose that I may have been mistaken in my former observation on this subject.