OXYGEN. 409 



energy is set free which is required by the life-processes taking place in the 

 tissues and cells. If all combustion took place in the lungs, then at a 

 single place the greater part of the total energy would be set free. The 

 tissues and cells could only secure for themselves a part of this energy by 

 means of certain cleavage-processes. An examination of the gases in the 

 blood would necessarily decide this question. If the oxygen actually 

 combined with the combustible substances directly in the lungs, then it 

 was certainly to be expected that the blood itself would contain but 

 little if any oxygen. This idea appealed to Magnus, 1 who analyzed the 

 gases in blood and showed that a certain amount of oxygen was present 

 until the capillaries were reached and at this point a part of it began to 

 disappear. This proved beyond question that all of the combustion 

 processes could not take place in the lungs. It left undecided the 

 question whether the oxidation processes took place exclusively in the 

 blood, or whether oxygen passed through the walls of the blood-vessels 

 into the tissues. It is conceivable that the tissues constantly give up 

 these oxidizable substances to the blood. In fact, certain discoveries 

 support this assumption. If the supply of oxygen be entirely cut off 

 from an animal, it suffocates. Its blood then contains but traces of 

 oxygen. On exposing such blood to oxygen, the latter disappears in a 

 short time, and the amount of carbon dioxide in the blood increases. 

 The blood of an animal which has not been suffocated shows the same 

 phenomenon, but to a much less extent. Ludwig and Schmidt, 2 who 

 carried out these experiments, explained this discovery on the assumption 

 that oxidizable substances were constantly being given up to the blood 

 which immediately underwent combustion provided the supply of oxygen 

 were adequate. If this supply were cut off, these substances began to 

 accumulate in the blood. Now we know that the blood contains cells, 

 the white and red blood corpuscles, which themselves undergo metabolism, 

 and thereby may easily consume oxygen and yield carbon dioxide. The 

 above experiments, therefore, are not sufficient to prove satisfactorily 

 that the combustion takes place chiefly in the blood. Afonassiew 3 then 

 showed that, as a matter of fact, only the blood-corpuscles and not the 

 serum of a suffocated animal could take up oxygen in this way. The 

 assumption that the combustion takes place in the cells and tissues them- 

 selves was furthermore supported by the following experiment: Pfliiger 

 and Oertmann 4 removed the blood from a frog, washed out the last 

 blood corpuscles with a 0.75 per cent solution of common salt, and finally 



1 Ann. Physik. 40, 583 (1837); and 64, 177 (1845). 



2 Ber. iiber die Verhandl. der Sachs. Ges. Wissen. Leipzig. Math.-physikal Klasse, 

 19, 99 (1867). 



3 Ibid. 24, 253 (1872). 



4 E. Oertmann: Pfliiger's Arch. 15, 382 (1877); E. Pfliiger: ibid. 10, 251 (1875). 



