10.  On further considering the action of contagious matter, since the former part of this work was sent to the press; where I have asserted, in Sect.  XXII. 3. 3. that it is probable, that the variolous matter is diffused through the blood; I prevailed on my friend Mr. Power, surgeon at Bosworth in Leicestershire to try, whether the small-pox could be inoculated by using the blood of a variolous patient instead of the matter from the pustules; as I thought such an experiment might throw some light at least on this interesting subject.  The following is an extract from his letter:—­

“March 11, 1793.  I inoculated two children, who had not had the small-pox, with blood; which was taken from a patient on the second day after the eruption commenced, and before it was completed.  And at the same time I inoculated myself with blood from the same person, in order to compare the appearances, which might arise in a person liable to receive the infection, and in one not liable to receive it.  On the same day I inoculated four other children liable to receive the infection with blood taken from another person on the fourth day after the commencement of the eruption.  The patients from whom the blood was taken had the disease mildly, but had the most pustules of any I could select from twenty inoculated patients; and as much of the blood was insinuated under the cuticle as I could introduce by elevating the skin without drawing blood; and three or four such punctures were made in each of their arms, and the blood was used in its fluid state.

“As the appearances in all these patients, as well as in myself, were similar, I shall only mention them in general terms.  March 13.  A slight subcuticular discoloration, with rather a livid appearance, without soreness or pain, was visible in them all, as well as in my own hand. 15.  The discoloration somewhat less, without pain or soreness.  Some patients inoculated on the same day with variolous matter have considerable inflammation. 17.  The discoloration is quite gone in them all, and from my own hand, a dry mark only remaining.  And they were all inoculated on the 18th, with variolous matter, which produced the disease in them all.”

Mr. Power afterwards observes, that, as the patients from whom the blood was taken had the disease mildly, it may be supposed, that though the contagious matter might be mixed with the blood, it might still be in too dilute a state to convey the infection; but adds at the same time, that he has diluted recent matter with at least five times its quantity of water, and which has still given the infection; though he has sometimes diluted it so far as to fail.

The following experiments were instituted at my request by my friend Mr. Hadley, surgeon in Derby, to ascertain whether the blood of a person in the small-pox be capable of communicating the disease.  “Experiment 1st.  October 18th, 1793.  I took some blood from a vein in the arm of a person who had the small-pox, on the second day of the eruption, and introduced a small quantity of it immediately with the point of a lancet between the scars and true skin of the right arm of a boy nine years old in two or three different places; the other arm was inoculated with variolous matter at the same time.