AFFINITY OF THE BLOOD FOR OXYGEN. 837 



gen, therefore, is also absorbed by blood in larger proportion than by 

 water, which can only take up 1.5 volumes, whilst blood can be made 

 to absorb 5 volumes per cent. 



It is plain, that both oxygen and carbonic acid are held in the blood, 

 not merely by its solvent power, as was supposed from the experiments 

 of Magnus, because he obtained those gases from the blood, by placing 

 it under an air-pump, or by displacing them with streams of hydrogen ; 

 but that it is in part, and in great part, held in it by special chemical 

 affinities. It is, moreover, evident that the absorption of oxygen by 

 the blood, depends on one kind of chemical affinity, and that of car- 

 bonic acid, on another. 



The oxygen is supposed almost entirely to enter into chemical com- 

 bination, essentially with some constituent of the red corpuscles ; for 

 although, as shown by its relative effects on dark clots, the serum may 

 contain variable quantities of oxygen, yet neither it nor the liquor 

 sanguinis, can absorb more oxygen than pure water. (Berzelius.) That 

 the oxygen is chemically combined is, moreover, inferred from the 

 fact, that pyrogallic acid, which has an extraordinary affinity for this 

 gas, does not withdraw it. when injected in solution into the blood, but 

 appears unaltered in the urine. The extreme affinity of blood for 

 carbonic acid, though partly due to the solubility of that gas in water, 

 may be partly owing to some special absorptive power in the albumi- 

 noid or other organic constituents ; but it is in a marked degree de- 

 pendent on the carbonate, or perhaps rather on the phosphate of soda, 

 which exists in considerable quantities in the liquor sanguinis. 



The special affinity of the red corpuscles for oxygen, has been at- 

 tributed to the iron contained in them, that element being supposed to 

 be in the condition of a sesquioxide in the corpuscles of arterial blood, 

 and of a carbonate of a protoxide in those of venous blood, the oxygen, 

 it is said, being displaced by the carbonic acid, which preponderates in 

 venous blood, and is the source of the carbonate above mentioned. 

 (Liebig.) It has, indeed, been alleged that the fibrin is concerned in 

 this transportation of the oxygen through the circulation, it having 

 been supposed to be in a higher state of oxidation in arterial than in 

 venous blood. But the spectrum analysis of the blood, proving that 

 oxygen produces such remarkable changes in the relations of the cru- 

 orin to luminous rays, would lead to the conclusion, that it is this col- 

 oring substance of the red corpuscles, which is the real carrier of 

 oxygen through the blood. Furthermore, it has been shown that the 

 blood corpuscles even absorb ozone, which is oxygen in a peculiar con- 

 dition, with great avidity, and yield it up to oxidizable substances 

 when brought into contact with them; the cruorin is also specially 

 concerned in this reaction. In animals provided with a distinct circu- 

 lation and red blood, the activity of the respiratory function is closely 

 related to the number and dimensions of the colored corpuscles in the 

 blood ; for these are few and large in the Cold-blooded, whilst they 

 are greatly increased in number and diminished in size in the Warm- 

 blooded Vertebrata. The latter arrangement provides for an enor- 

 mous multiplication of the surfaces of the corpuscles. 



The entrance of oxygen into the blood being thus due to the joint 



