Page:Proceedings of the Royal Society of London Vol 1.djvu/535

Rh For this purp08e, the ves5el which serves as condensing worm-tub to the ﬁrst distillation requires to be ﬁtted with a head and a receiver, all perfectly air-tight; and it may with most convenience be so con- structed, that, by application of heat in the ﬁrst instance to this ves— sel, the water within maybe made to boil completely, so that the air within it will be thereby expelled, and, by a valve or cock, may be prevented from ramming when the heat is withdrawn.

The experiments here detailed relate, in the ﬁrst place, to the relative capacities of venous and arterial blood for heat; secondly, the comparative temperature of these ﬂuids in different parts of the body during life is attempted to be ascertained; and thirdly, the author states those conclusions which he thinks may be drawn from his experiments.

In his ﬁrst experiments he endeavours to discover the relative capacities by the times of cooling equal volumes of venous and arterial blood, regard being also had to the speciﬁc gravities of each. When blood was taken from the jugular vein of a lamb, and after the ﬁbrin had been separated from it by stirring with a wooden spatula, its speciﬁc gravity was found to be 1050, that of arterial blood from the same lamb, similarly treated, being 1047. The quantity of each taken for experiment was the same, contained in the same vessel, and heated to the same degree. An equal quantity of water in this vessel had cooled from 120° to 80° in ninety-one minutes ; arterial blood cooled, through the same interval, in eighty-nine minutes; and venous blood in eighty-eight minutes : and hence the author infers the capacity of venous blood to be to that of arterial as 92 to 93'7, that of Water being 100. By other experiments made on various mixtures of these ﬂuids with each other at different temperatures, he estimates the proportion to be 93 to 93'7.

In subsequent trials on the rates of cooling observed in blood that still contained its fibrin, Dr. Davy estimated the capacities of venous and arterial blood to be as 90 to 91.

The next experiments were upon the proportional heat lost in a. given time by mixtures of either kind of blood with water, due allowance being made, as before, for the difference of their speciﬁc gravities (viz. 1050 and 1049).

In this mode of trial the proportions were nearly reversed, the capacity of venous blood appearing to be 95-4, whilst that of arterial was no more than 94'8. But the author observes, that these trials admit of less accuracy than the preceding; and he would be inclined to consider the third set of experiments as most entitled to conﬁdence.

Dr. Davy’s ﬁrst experiments on the actual temperatures of venous and arterial blood in the living body, were made at the great vessels of the neck in lambs, sheep, and mien; and in each a difference was