In constitutions predisposed to scrofula, how frequently we see the inoculated Small-pox rouse into activity that distressful malady. This circumstance does not seem to depend on the manner in which the distemper has shown itself, for it has as frequently happened among those who have had it mildly, as when it has appeared in the contrary way. There are many, who from some peculiarity in the habit resist the common effects of variolous matter inserted into the skin, and who are in consequence haunted through life with the distressing idea of being insecure from subsequent infection. A ready mode of dissipating anxiety originating from such a cause must now appear obvious. And, as we have seen that the constitution may at any time be made to feel the fertile attack of Cow-pox, might it not, in many chronic diseases, be introduced into the system, with the probability of affording relief, upon well-known physiological principles? Although I say the system may at any time be made to feel the febrile attack of Cow-pox, yet I have a single instance before me where the virus acted locally only, but it is not in the least probable that the same person would resist the action both of Cow-pox virus and the variolous. FOOTNOTES: [Footnote 23: From _An Inquiry into the Cause and Effects of the Variolae Vaccinae_.] XXI COUNT RUMFORD 1753-1814 _Sir Benjamin Thompson, Count Rumford, was born in Woburn, Massachusetts, March 26, 1753, a member of an old New England family. After a very romantic youth and early manhood in which he underwent many exciting adventures as a British loyalist at the time of the American Revolution, he was sent to England with despatches by the British expeditionary authorities and there found employment in the office of the Secretary of State. After the close of the Revolution he went to Bavaria, where he became Minister of War and Grand Chamberlain. In 1791 he was made a count of the Holy Roman Empire. In 1796 President Adams invited him to return to America to become an inspector of artillery, but he declined; and at about the same time he became interested in problems of heat, light, and fuel. His suggestions ultimately became the basis for the doctrine of the conservation of energy. He died at Auteuil, August 25, 1814._ THE NATURE OF HEAT[24] After I had long meditated upon a way of putting this interesting problem entirely out of doubt by a perfectly conclusive experiment, I thought finally that I had discovered it, and I think so still. I argued that if the existence of caloric was a fact, it must be absolutely impossible for a body or for several individual bodies, which together made one whole, to communicate this substance continuously to various other bodies by which they were surrounded, without this substance gradually being entirely exhausted.