THE CHEMISTRY OF RESPIRATION 



1057 



desired to compare the oxygen contents of two samples of blood, e.g. of arterial and venous 

 blood. For this purpose 1 c.c. of the arterial blood is introduced into one bottle and 1 c.c. 

 of the venous blood into the other bottle, in each case under 1| c.c. of weak ammonia. The 

 bottles are then placed on the apparatus and immersed in the water bath until no change 

 occurs in the height of the column of oil. The two taps are then closed and the apparatus 

 is vigorously shaken. The blood on each side is laked, and in contact with the air in 

 the bottles becomes completely saturated with oxygen. No carbon dioxide is given off, 

 since this combines with the weak ammonia. If the two bloods contain the same amount 

 of oxyhsemoglobin no difference will be produced in the level of the oil in the two tubes. 

 If, however, one be arterial and the other venous, the venous blood will absorb more 

 oxygen from its bottle than the arterial blood from its side of the apparatus, so that the 

 oil will rise in the tube on the side of the venous blood. From the amount of rise the 

 difference in the amount of oxygen taken up by the blood on the two sides can be reckoned 

 and this figure will express the relative saturation of the haemoglobin in the two samples 

 of blood. 



For clinical purposes it is possible to work with 0-1 c.c. of blood. Fig. 494 B repre- 

 sents the form of apparatus devised by Barcrof t for dealing with these minute quantities. 

 The principle of the apparatus is the same as that of the larger type. 



The condition of the gases in the blood can be judged by the amount of 

 gas which the blood will take up when exposed to different pressures of the 

 gas. If a gas is in simple solution the amount of it dissolved varies directly 

 with the pressure. Thus, if water takes up a certain bulk of a gas at a given 

 temperature and pressure, it will take up twice as much if the pressure of 

 the gas be doubled. Since the volume of a gas varies inversely as the 

 pressure, we may say that a fluid will dissolve the same volume of gas 

 whatever the pressure. The absorption coefficient of a liquid for a gas is 

 expressed by the number of cubic centimetres of gas which will be taken 

 up at C. by 1 c.c. of the liquid when the gas is at a pressure of 760 mm. 

 Hg. The absorption coefficient diminishes with rise of temperature. The 

 following Table represents the absorption coefficients for oxygen, carbon 

 dioxide, carbon monoxide, and nitrogen, in water at various temperatures 

 between and 40 C. : 



From this Table we see that 100 c.c. of water at C. will absorb 

 4-89 c.c. oxygen at 760 mm. Hg., i.e. at one atmosphere. If the pressure be 

 raised to two atmospheres the volume of gas absorbed will be the same, but 

 if these gases be measured at the original pressure, i.e. at one atmosphere, 

 the amount dissolved will be 9-78 volumes. If therefore we plot out the 

 absorption of the gas on a curve of which the ordinates represent the amount 

 of gas dissolved and the abscissa the different pressures of the gas, we shall 

 find that the curve is a straight line. The relation between the amount 



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