THEORY. 387 



vations of Magnus and Marchand, to which we have already 

 referred, and according to which the fresh blood exhibited no 

 chemical attraction from oxygen, might incline us to believe that 

 all the oxygen absorbed by the blood in the lungs passed un- 

 changed, that is to say, uncombined, into the capillaries of the 

 greater circulation, and from thence into the parenchyma of the 

 organs. This, however, is by no means the case, and we have 

 already given the reasons, which seem to show that a part of the 

 absorbed oxygen enters into chemical combinations even in the 

 arterial blood. We need here only refer to the peculiar relation of 

 the crystalline substance of the blood towards gases [see note to 

 vol. i, p. 373 in the Appendix], and to Liebig's apodictic proof, that 

 as the blood considered as a fluid can mechanically absorb only a 

 very small portion of oxygen, the greatest part of the oxygen which 

 disappears during respiration must of necessity be chemically 

 absorbed. 



The very careful and admirable experiments of G. Liebig* 

 appear at first sight to oppose the idea of a chemical absorption 

 of the oxygen in the lungs ; for he found that the differences of 

 temperature in the different parts of the circulating system, 

 including both the arterial and the venous systems, were solely 

 referrible to the physical laws of the radiation of heat, &c., and 

 that in the lungs especially, the blood not only undergoes no 

 elevation, but even a slight depression of temperature. 



Here, therefore, we obtain for the first time, through G. Liebig's 

 investigations, a direct confirmation of the early hypothesis, that 

 the blood is cooled in the lungs by respiration. This fact appears, 

 as has already been stated, to stand in direct opposition to the 

 assumption that the oxygen is chemically absorbed, at all events 

 in part, in the arterial system. This discrepancy is, however, 

 merely apparent, as we may readily perceive, when we consider 

 that only a part of the oxygen that enters the blood is chemically 

 absorbed, that a great part of the free heat is consumed in the 

 restoration of the carbonic acid to its gaseous form and in the 

 evaporation of water, that the specific heat of water is very great, 

 and that the difference of temperature between the blood in the 

 left side of the heart and that of the right side is extremely small. 

 If we follow G. Liebig's experiments in their details, more 

 especially in reference to the testing of the methods of observation, 

 and observe how the temperature of the blood in the different 



* Ueber d. Temperaturunterschiede d. venosen u. arteriellen Bluts. Inaug. 

 Abh. d. Med. Fac, zu Giessen vorgel. 1853. 



2 C2 



