THE OXYGEN IN BLOOD 525 



the blood could be displaced by an equal volume of carbon 

 monoxide. Hoppe-Seyler then succeeded in crystallising haemo- 

 globin, and proved that it combined with oxygen, but on exposure 

 to a vacuum again yielded up the gas. A year or two later, 

 in 1864, Stokes discovered that reducing agents abstracted the 

 oxygen from haemoglobin, and thereby altered its colour and 

 spectrum. 



The blood can be divided by means of the centrifugal machine 

 into plasma and corpuscles, and a similar separation can be effected 

 by cooling horse's blood and allowing the corpuscles to subside. 

 These two portions show a marked difference in their relation to 

 oxygen. The plasma contains but a small amount, and this is 

 dissolved in proportion to the pressure, according to Henry's law ; 

 thus the quantity of oxgyen in plasma which has been shaken with 

 air at the ordinary temperature and pressure is about 0-65 volumes 

 per cent., a value not very different from that obtained with water. 

 The whole blood, when treated in a similar manner, absorbs 18*5 

 to 24 volumes per cent. ; the first figure is the average for human 

 blood according to Haldane's experiments, the latter the result 

 obtained by Bohr for dog's blood. These figures, therefore, repre- 

 sent the oxygen capacity of the blood of man and dog respectively. 

 There is thus no doubt that oxygen is present in blood in the states 

 of simple solution and chemical combination ; the latter is the 

 predominant state and requires further consideration. 



According to Bunge's determinations, 100 parts of red corpuscles 

 contain 26 parts of haemoglobin and 63 parts of water ; this 

 would correspond to a 41 per cent, solution, but in making this 

 statement it must be remembered that the haemoglobin is probably 

 not present in simple solution in the red corpuscles. The blood 

 considered as a whole contains about 14 per cent, of haemoglobin, 

 which is present only in the red corpuscles. It is with the blood 

 that the gaseous exchange takes place ; the red corpuscles are the 

 oxygen-carriers, they yield up oxygen to the plasma, which in 

 turn supplies the tissues according to their needs. The most 

 important question to be considered later is the 'pressure of the 

 oxygen in the red corpuscles, whereby the pressure in the plasma 

 is maintained during its course through the systemic circulation. 



It is necessary to determine the amounts of oxygen taken up 

 under different pressures and at a constant temperature. The 

 last factor is important, especially when low pressures of oxygen 



