the measles were in a farm house in the neighbourhood.  Miss H.’s arm less inflamed than yesterday.  On the 14th Miss L.’s fever great, and the eruption universal.  The arm appears to be healed.  Miss H.’s arm somewhat redder.  They were now put into separate rooms.  On the 15th Miss L.’s arms as yesterday.  Eruption continues.  Miss H.’s arms have varied but little. 16th, the eruptions on Miss L. are dying away, her fever gone.  Begins to have a little redness in one arm at the place of inoculation.  Miss H.’s arms get redder, but she has no appearance of complaint. 20th, Miss L.’s arms have advanced slowly till this day, and now a few pustules appear.  Miss H.’s arm has made little progress from the 16th to this day, and now she has some fever. 21st, Miss L. as yesterday.  Miss H. has much inflammation, and an increase of the red circle on one arm to the size of half a crown, and had much fever at night, with fetid breath. 22d, Miss L.’s pustules continue advancing.  Miss H.’s inflammation of her arm and red circle increases.  A few red spots appear in different parts with some degree of fever this morning, 23d.  Miss L. has a larger crop of pustules.  Miss H. has small pustules and great inflammation of her arms, with but one pustule likely to suppurate.  After this day they gradually got well, and the pustules disappeared.

In one of these cases the measles went through their common course with milder symptoms than usual, and in the other the measly contagion seemed just sufficient to stop the progress of variolous contagion, but without itself throwing the constitution into any disorder.  At the same time both the measles and small-pox seem to have been rendered milder.  Does not this give an idea, that if they were both inoculated at the same time, that neither of them might affect the patient?

From these cases I contend, that the contagious matter of these diseases does not affect the constitution by a fermentation, or chemical change of the blood, because then they must have proceeded together, and have produced a third something, not exactly similar to either of them:  but that they produce new motions of the cutaneous terminations of the blood-vessels, which for a time proceed daily with increasing activity, like some paroxysms of fever, till they at length secrete or form a similar poison by these unnatural actions.

Now as in the measles one kind of unnatural motion takes place, and in the small-pox another kind, it is easy to conceive, that these different kinds of morbid motions cannot exist together; and therefore, that that which has first begun will continue till the system becomes habituated to the stimulus which occasions it, and has ceased to be thrown into action by it; and then the other kind of stimulus will in its turn produce fever, and new kinds of motions peculiar to itself.