1106 



PHYSIOLOGY 



acidification of the blood causes the evolution of a certain amount of oxygen. The 

 results obtained for carbon dioxide are not so accurate as those for the oxygen, owing to 

 the larger error introduced by the increased solubility of this gas in watery media. 



The same apparatus may be used as a differential blood-gas manometer, where it is 

 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. pf the venous blood into the other bottle, in each case under \\ 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 oilin 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 degree 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. 506 B represents 

 the form of apparatus devised by Barcroft 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 iOO 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 



