ITS GASES. 191 



favour of, and others opposed to the presence of gases in solution 

 in the blood. The question was. however, decided about ten years 

 ago, by the experiments of van Enschut, Bischoff, John Davy, and 

 especially Magnus, which shewed that free gases are contained in 

 solution in perfectly fresh blood, both arterial and venous ; more 

 recently, and by means of simpler experiments, Magnus * has con- 

 firmed his former observation, that, in addition to carbonic acid, 

 both free oxygen and nitrogen occur in the blood. According to 

 the earlier investigations of Magnus, arterial and venous blood 

 contain nearly equal quantities of nitrogen; in the former, the 

 oxygen is to the carbonic acid (by volumes) as 6 : 16, and in the 

 latter as 4 : 16; hence, therefore, there is relatively more oxygen 

 in arterial than in venous blood. His more recent experimentsf 

 determine not merely the ratio of the volumes of the gases to one 

 another, but also to the volume of the blood ; they show that at 

 all events in the blood of calves, oxen, and horses, there are always 

 in solution from 10 to 12'5-g- (by volume) of oxygen, and from 1*7 

 to 3'3-g- (by volume) of nitrogen. According to an experiment of 

 Magendie's, venous blood contains 78, and arterial only 66 J (by 

 volume) of carbonic acid. The oxygen of the blood may also be 

 almost entirely extracted in vacuo, as well as expelled by other 

 gases, as for instance, hydrogen and carbonic acid ; whence it is 

 sufficiently clear that it is only mechanically absorbed in the blood, 

 and not in a state of chemical combination. Since the blood, 

 according to the experiments of Magnus, is capable of absorbing 

 1J times its volume, or 150 of carbonic acid, it may, at first sight, 

 appear strange that the circulating blood is not found to be more 

 impregnated with carbonic acid, and that in respiration there is 

 only little more oxygen absorbed than carbonic acid given off; but 

 when we consider that in respiration the relations of the concurrent 

 gases are altogether different from what they are in our experiments 

 (in which we shake pure atmospheric air or pure carbonic acid 

 with the blood), this difficulty is at once removed. 



In connexion with the occurrence of free oxygen in the blood, 

 there is an important, and indeed even yet a scarcely decided 

 question whether, at all events, a portion of the oxygen that finds 

 its way through the lungs into the circulation, does not at once 

 chemically combine, in the arterial system, with some of the con- 

 stituents of the blood. Marchand attempted to decide this question 

 by certain experiments, and Magnus by a calculation based on 



* Fogg. Ann. Bd. 36, S. 685 ff. 

 t Ibid. Bd. 56, S. 177-206. 



