CIRCULATING SYSTEM. 345 
ments of Darwin, already alluded to, demonstrate, that 
there is no air in the blood while confined in the proper 
vessels, and render it prebable that the air which appears, 
when the blood is placed under the exhausted receiver of an 
air-pump, has been mixed with the blood upon leaving the 
vessels and passing through the atmosphere *. 
Chemical Constitution.—The serum from which the clot 
has been removed, is more fluid than the blood itself, but 
retains its taste and smell. It is slightly alkaline, and con- 
sequently renders vegetable blues green. When heated to 
the temperature of about 160°, it coagulates, and if this coa- 
gulum be cut into thin slices, a fluid oozes out, which is term- 
ed Serosity. 'The coagulum has all the properties of coa- 
gulated albumen. The serosity still contains a considerable 
portion of albumen, whose properties are much modified by 
the salts with which it is combined. The following are the 
contents of the serum, as stated by different chemists :— 
Marcerrt. BeERZELIUS. 
Water, - = - 900.0 905.0 
Albumen, - = 86.8 80.0 
Muriate of potash and soda, - - 6.6 6.0 
Subcarbonate of soda, = - - 1.65 
Sulphate of potash, - - - 0.35 
Earthy phosphate, - - 0.60 
Lactate of soda united with animal matter, 4.0 
Soda, phosphate of soda, and a little animal matter, 4,1 
* The following, among many of his experiments, may be quoted :— 
«¢ A part of the jugular vein of a sheep, with the blood in it, was included 
between two 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 
dry, 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.” — 
Phil. Trans. 1774, p. 345. Similar experiments, with the same results, 
were repeated on the blood in the vena cava inferior of a large swine, 
