158 RESPIRATION'. 



takes place in the capillary system and which is one of the indispensable conditions of 

 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 function as re- 

 spiratory organs. As it is the continuance of this transformation of oxygen into carbonic 

 acid, after the blood is drawn from the vessels, which interferes with the ordinary analy- 

 sis of the blood for gases, we might expect to extract all the oxygen if we could imme- 

 diately saturate the blood with carbonic oxide. The preliminary experiments of Ber- 

 nard on this point are conclusive. He ascertained that, by mixing carbonic oxide in suf- 

 ficient quantity with a specimen of fresh arterial blood, in about two hours, all the oxy- 

 gen which it contained was displaced. Introducing a second quantity of carbonic oxide 

 after two hours, and leaving it in contact with the blood for an hour, a quantity of oxy- 

 gen was removed so small that it might almost be disregarded. A third experiment on 

 the same blood failed to disengage any oxygen or carbonic acid. 



The view entertained by Bernard of the action of carbonic oxide in displacing the 

 oxygen of the blood is, that the former gas has a remarkable affinity for the blood-corpus- 

 cles, in which nearly all the oxygen is contained, and when brought in contact with 

 them unites with the organic matter, setting free the oxygen, in the same way that the 

 acid entering into the composition of a salt is set free by any other acid which has a 

 stronger affinity for the base. There is every reason to suppose that this view is correct, 

 as carbonic oxide is much less soluble than oxygen and as it has the property of dis- 

 engaging this gas only from the blood, leaving the other gases still in solution. 



As carbonic oxide displaces the oxygen alone, it is necessary to resort to some other 

 process, in addition to this, to disengage the other gases contained in the blood. It is 

 only necessary to arrest the action of the corpuscles upon the oxygen, and then the 

 gases may be set free by the air-pump or any method which may be convenient. The 

 method adopted by Lothar Meyer, Bernard, Ludwig, and Grebant for the disengagement 

 of all the gases contained in the blood is first to displace the oxygen by carbonic oxide, 

 using about two-thirds of gas by volume to one-third of blood, then to attach the tube 

 to a column of mercury and subject the blood to the barometric vacuum, which sets free 

 the carbonic acid and the nitrogen. The results obtained by this method correspond 

 with our ideas concerning the nature of the respiratory process; and analyses of the 

 blood taken at different periods show variations in the quantities of oxygen in the ar- 

 terial, and carbonic acid in the venous blood, corresponding with some of the variations 

 which we have noted in the loss of oxygen and gain of carbonic acid in the air in res- 

 piration. 



In drawing the blood for analysis, Bernard takes the fluid directly from the vessels by 

 a syringe and passes it under mercury into a tube, in such a way that it does not come in 

 contact with the air. In this tube, which is graduated, the blood is brought in contact 

 with carbonic oxide, which displaces the oxygen from the corpuscles and prevents the 

 formation of carbonic acid at the expense of a portion of the oxygen. The tube is then 

 connected with an apparatus by which the atmospheric pressure is removed. In this way, 

 nearly all the gases contained in the blood are disengaged ; but, according to most ob- 

 servers, a small quantity of carbonic acid remains in the blood in combination. This may 

 be removed by the introduction into the apparatus of a small quantity of tartaric acid. 

 It is justly remarked by Bert, in his admirable work on respiration, that, as the appa- 

 ratus for the exhaustion of air has been made more and more nearly perfect, the quantity 

 of carbonic acid in combination has seemed less and less. By far the greatest quantity of 

 the excrementitious carbonic acid in the blood is extracted by the removal of atmospheric 

 pressure in the most carefully-perfected apparatus. 



The analyses of Bernard, who obtained from fifteen to twenty per cent, of oxygen in 

 volume from the arterial blood, show the great imperfection of the process employed by 

 Magnus, who obtained from the arterial blood of horses and calves a mean of but 2*44 

 per cent, of oxygen. It does not seem necessary, therefore, to discuss the criticisms of 



