ANALYSIS OF THE BLOOD FOR GASES. 157 



specimen of blood present great variations, dependent upon the length of time that the 

 blood has been allowed to stand before the estimate of the gases is made. As it is im- 

 possible to make this estimate immediately after the blood is drawn, on account of the 

 froth produced by agitation with a gas when the method by displacement is employed, 

 and the bubbling of the gas when extracted by the air-pump, this objection is fatal. It 

 is necessary to wait until the froth has subsided before attempting to make an accurate 

 estimate of the volume of gas given off. The following observation of Magnus illus- 

 trates this fact. The observation was on the human blood, six hours after it had been 

 thoroughly mixed with hydrogen : 



Blood of Man. Carbonic Acid. 



4-077 cubic inches. '013 cubic inches. 



3-650 " 0-781 " 



3-838 " 1-355 " 



After twenty -four hours, at the end of which time the blood had no odor : 



4-077 cubic inches. 1-517 cubic inches. 



3-650 " 1-456 " 



3-833 " 2-075 " 



The excess of carbonic acid found twenty-four hours after over the quantity found 

 six hours after, in the first and third specimens, is a little more than fifty per cent., while 

 in the second specimen it is very nearly one hundred per cent. In these analyses, the pro- 

 portion of oxygen is not given. The question naturally arises as to the source of the car- 

 bonic acid which was evolved during the last eighteen hours of the observation. This is 

 evident, when we consider one of the important properties of the blood. A number of 

 years ago, Spallanzani demonstrated that, in common with other parts of the body, fresh 

 blood removed from the body has, of itself, the property of consuming oxygen ; and 

 W. F. Edwards has shown that the blood will exhale carbonic acid. In 1856, Harley, 

 by a series of ingenious experiments, found that blood, kept in contact with air in a 

 closed vessel for twenty -four hours, consumed oxygen and gave off carbonic acid. More 

 recently, Bernard has shown that, for a certain time after the blood is drawn from the 

 vessels, it will continue to consume oxygen and exhale carbonic acid. If all the carbonic 

 acid be removed from a specimen of blood by treating it with hydrogen, and if it be 

 allowed to stand for twenty-four hours, another portion of gas can be removed by again 

 treating it with hydrogen, and still another quantity by treating it with hydrogen a third 

 time. From these facts it is clear that, in the experiment of Magnus, the excess of car- 

 bonic acid involved a post-mortem consumption of oxygen ; and no analyses made in the 

 ordinary way, by displacement with hydrogen or by the air-pump, in which the blood 

 must necessarily be allowed to remain in contact with oxygen for a number of hours, can 

 be accurate. The only process which can give us a rigorous estimate of the relative quan- 

 tities of oxygen and carbonic acid in the blood is one in which the gases can be esti- 

 mated without allowing the blood to stand, or in which the formation of carbonic acid 

 in the specimen, at the expense of the oxygen, is prevented. All others will give a less 

 quantity of oxygen and a greater quantity of carbonic acid than exists in the blood cir- 

 culating in the vessels or immediately after it is drawn from the body. 



A solution of this important and difficult problem in the analysis of the blood has been 

 attained by Bernard. This observer made a great number of experiments in the hope of 

 discovering some means by which the post-mortem consumption of oxygen by the blood- 

 corpuscles could be arrested. He found, finally, that carbonic oxide, one of the most active 

 of the poisonous gases, had a remarkable affinity for the blood-corpuscles. When taken 

 into the lungs, it is absorbed by and becomes fixed in the corpuscles, effectually prevent- 

 ing the consumption of oxygen and the production of carbonic acid, which normally 



