536 I'HILOSOI'HICAL TRANSACTIONS. [aNNO 1774. 



XXKVL Experiments on Animal Fluids in the Exhausted Receiver. By D. 

 Darwin, M. D., of Litchfield, p. 344. 



The ancient opinion, that air exists in some of the blood vessels, was ex- 

 ploded by the discovery of the circulation. But many of our modern theorists 

 seem to have conceived, that an elastic vapour of some kind exists in the blood 

 vessels, as they have ascribed the lunar and equinoctial diseases to the variations 

 of atmospheric pressure. This opinion seems to have arisen from observing, 

 that the skin rises, and that the vessels are distended, even to bursting, under a 

 cupping-glass; when the pressure of the atmosphere is taken off from one part, 

 and continues to act on all the remaining surface of the body: and would indeed, 

 at first sight, appear to be demonstrated by the following experiments. About 

 4 oz. of blood were taken from the arm of one of the attendants, and immedi- 

 ately put under the receiver of an air-pump; and, as the air was exhausting, the 

 blood began to swell, and to rise in bubbles, till it occupied above 10 times its 

 original space. 



As false reasoning is, in no science, of more dangerous consequence than in 

 that of medicine. Dr. D. persuaded himself that the removal of this error might 

 be thought worthy the attention of the r. s. In April 1772, Mr. Young, an 

 ingenious surgeon at Shiffnal in Shropshire, and Mr. Waltire, an accurate lec- 

 turer in natural philosophy, made, at his request, the following experiments. 

 1 . A part of the jugular vein of a sheep, with the blood in it, was included be- 

 tween 1 strict ligatures, during the animal's being alive, and being cut out with 

 the ligatures, was immediately put into a glass of warm water, and placed in the 

 receiver of an air-pump, it sunk to the bottom of the water, and would not rise 

 when the air was diligently exhausted. It was then wiped drj', and laid on the 

 brass floor of the receiver, and the air again exhausted, but there was not the 

 least visible expansion of the vein, or its contents. 2. A ligature was put round 

 the neck of the gall-bladder of the same animal, as soon as it was slaughtered; 

 the gall-bladder, with the bile in it, was first put into water, in which it sunk, 

 and was placed in the exhausted receiver of the air-pump; and was afterwards 

 wiped dry, and laid on the brass plate at its bottom, as in the former experiment; 

 but in neither case, on the greatest degree of exhaustion, did it show the least 

 alteration of its bulk. 3. The neck of the urinary bladder of the same animal 

 was well secured with a ligature, and contained about 2 or 3 oz. of fluid. The 

 bladder sunk immediately on being put into warm water; but, on exhausting the 

 receiver, many silver-like globules appeared on its surface; and it soon showed 

 manifest signs of expansion, and rose to the top of the vessel. The same expe- 

 riment was tried with it wiped dry, and laid on the floor of the receiver, and 

 the result was, that its expansion and contraction were very perceptible to 

 the eye. 



