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A TEXTBOOK OF PHYSIOLOGY 



When these values are compared with the amounts of the gases 

 obtained from the blood, it is found that only nitrogen is in true 

 physical solution. Of the carbon dioxide and oxygen the greater part 

 is in chemical combination; yet, inasmuch as considerable quantities 

 of these gases can be pumped from the blood, this chemical combination 

 is of an easily dissociable (weak) form. When the blood is submitted 

 to the vacuum pump, the gases do not come off in proportion as the 

 pressure is reduced indeed, with the first reduction of pressure little 

 gas comes off but when the pressure is considerably lowered, and the 

 blood warmed, the gases come off with a rush, and the blood " boils "" 

 and froths in a very striking way. 



The oxygen is combined with the red corpuscles, as is shown by the 

 fact that, when the corpuscles are removed from the plasma, the 

 latter only takes up that amount of oxygen which is dissolved 

 in accordance with the coefficient of absorption. It is to the 

 haemoglobin of the corpuscles that the oxygen is loosely attached, and 



A A A A A 



20 



40 



100 



Fio. 136. A SERIES OF TONOMETEBS INDICATING THE PRESSURE GF OXYGEN TO 

 WHICH THE BLOOD is EXPOSED. (Barcroft.) 



the amount of oxygen taken up by the blood over and above that 

 which can be absorbed by purely physical means depends upon the 

 amount of haemoglobin present. 



Many experiments have been made to ascertain the specific oxygen 

 capacity of the blood. The earliest observations were made correctly 

 on the blood itself; then it was thought better to separate the haemo- 

 globin and, purifying this, determine its combining powers. From 

 the results so obtained it was. concluded that a given amount of haemo- 

 globin always combined with a definite amount of oxygen (1 grm. 

 of Hb with 1-34 c.c. of 2 ); 100 c.c. of human blood contains about 

 12 to 15 grms. Hb. 1-34 x 14 = 19, which is about the percentage of 

 oxygen found in arterial blood. Recent research, however, has shown 

 that the exact amount of oxygen depends upon a number of factors 

 e.g., the temperature, concentration of salts, and of carbon dioxide 

 in the blood. The blood is exposed to an atmosphere containing a 

 known concentration (pressure) of oxygen, and thoroughly shaken 

 with this (Fig. 136). It is then withdrawn without contact with the 



