move her arm or hand. The rate of these vibrations was usually
about 80 in a minute; but were much increased from any slight
cause of general irritation.
Upon examination of the carotids, they seemed to be somewhat dilated, for about half an inch in length; but in other parts they were not larger than natural. The involuntary motions, which in this lady were confined to the left side, were not in any degree af- fected by pressure of the carotids on that side; but when the right carotid was strongly compressed, all the vibrations were uniformly stopped; which, says the author, hardly could occur but from -re- moval of undue pressure of the brain, and consequent excessive irri- tation.
Dr. Marcet, having been requested by Dr. Wollaston to examine whether the serous fluid, secreted in consequence of the application of a blister, could be impregnated with prussiate of potash, gave to a young woman five grains of this prussiate, every hour, till she had taken thirteen or fourteen such doses. After the fifth dose, when her urine became blue immediately by addition of sulphate of iron, a blister was applied, and the serum secreted in consequence was col- lected, whilst her urine still indicated the presence of the prussiate. But in this semm no prussiate could be detected.
Dr. Maroet also repeated Dr. VVollaston’s experiment on serum derived directly from the blood, but with this variation, that the blood was drawn by cupping; and he could not discover the presence of any prussiate.
The author observes, that in several instances in which prussiate of potash had been taken by other persons, it could not be detected in their urine. As some of those in whom it failed to appear were taking mercury at the time, he conjectured that the difference might possibly arise from that cause; but as in two other failures no mer- cury was present, he does not lay much stress on that conjecture.
Reply of Dr. Marcet on the same Subject.
This letter contains the details of experiments made several years since.
First. On the serum of blood, with a view to discover some easy means of detecting the presence of sugar added to it.
Secondly. Upon the blood of persons whose urine was known to contain sugar, for the purpose of determining whether it was also present in their blood.
Thirdly. Upon the blood of persons secreting, by urine, other ingredients, which had been swallowed for that purpOse, in order to ascer-
