I was the more struck with this disease, from finding it was taken notice of by Dr. Sydenham. He calls it a morbillous fever. I likewise find an account of it in the 2d article of the 5th volume of the Edinburgh Medical Essays. The words of the author, who is anonymous, are as follow. "During this measly season, several persons, who never had the measles, had all the symptoms of measles, which went off in a few days without any eruptions. The same persons had the measles months or years afterwards." Is this disease a common fever, marked by the reigning epidemic, and produced in the same manner, and by the same causes, as the variolous fever described by Dr. Sydenham, which he says prevailed at the same time with the small-pox? I think it is not. My reasons for this opinion are as follow. 1. I never saw it affect any but children, in the degree that has been mentioned, and such only as had never had the measles. 2. It affected whole families at the same time. It proved fatal to one of three children whom it affected on the same day. 3. It terminated in a pulmonary consumption in a boy of ten years old, with all the symptoms which attend that disease when it follows the regular measles. 4. It affected a child in one family, on the same day that two other members of the same family were affected by the genuine measles. 5. It appeared on the usual days of the genuine measles, from the time the persons affected by it were exposed to its contagion. And, 6. It communicated the disease in one family, in the usual time in which the disease is taken from the genuine measles. The measles, then, appear to follow the analogy of the small-pox, which affects so superficially as to be taken a second time, and which produce on persons who have had them what are called the nurse pock. They follow likewise the analogy of another disease, viz. the scarlatina anginosa. In the account of the epidemic for 1773, published in the third volume of the Edinburgh Medical Essays, we are told, that such patients as had previously had the scarlet fever without sore throats, took the sore throat, and had no eruption, while those who had previously had the sore throat had a scarlet eruption, but the throat remained free from the distemper. All other persons who were affected had both. From these facts, I have taken the liberty of calling it the _internal measles_, to distinguish it from those which are _external_. I think the discovery of this new state of this disease of some application to practice.