152 CHANGES OP AIR AND BLOOD IN RESPIRATION. 



displacement is employed, and the bubbling of the gas when extracted by the 

 air-pump, the objection is very serious. It is necessary to wait until the froth 

 has subsided before attempting to make an accurate estimate of the volume 

 of gas given off. This fact is illustrated by one of the published observations 

 of Magnus upon three different specimens of human blood. In this observa- 

 tion the specimens of blood were thoroughly mixed with hydrogen. The 

 excess of carbon dioxide found twenty-four hours after, over the quantity 

 found six hours after, in two specimens, was a little more than fifty per cent., 

 while in one specimen it is very nearly one hundred per cent. In these analyses 

 the proportion of oxygen was not given. The question naturally arises as to 

 the source of the carbon dioxide which was evolved during the last eighteen 

 hours of the observation. The question is readily solved by certain experi- 

 ments, which are by no means of recent date, although the results of these 

 observations have been confirmed by modern investigations. A number of 

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

 body, fresh blood has, of itself, the property of consuming oxygen ; and W. F. 

 Edwards has shown that the blood will exhale carbon dioxide. In 1856, Har- 

 ley found that blood, kept in contact with air in a closed vessel for twenty- 

 four hours, consumed oxygen and gave off carbon dioxide. 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 carbon dioxide. If 

 all the carbon dioxide 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 the blood 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 carbon 

 dioxide 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 is allowed to remain in contact with oxygen for 

 a number of hours, can be accurate. The only process which can give a 

 rigorous estimate of the relative quantities of oxygen and carbon dioxide 

 in the blood is one in which the gases can be estimated without allowing 

 the blood to stand, or in which the formation of carbon dioxide, at the ex- 

 pense of the oxygen in the specimen, is prevented. All others will give a 

 less quantity of oxygen and a greater quantity of carbon dioxide than exists 

 in the blood circulating in the vessels or immediately after it is drawn from 

 the body. 



Carbon monoxide, one of the most active of the poisonous gases, has a re- 

 markable affinity for the blood-corpuscles. When taken into the lungs, it is 

 absorbed by and becomes fixed in the corpuscles, preventing the consumption 

 of oxygen and the production of carbon dioxide, which normally take place 

 in the capillary system and which are indispensable conditions 01 nutrition. 

 The mechanism of poisoning by the inhalation of this gas is by its fixation 

 in the blood-corpuscles, their consequent paralysis, and the arrest of their 

 action as oxygen-carriers. As it is the -continuance of this transformation 

 of oxygen into carbon dioxide, after the blood is drawn from the vessels, 



