CHANGES IN AIR AND BLOOD IN RESPIRATION. 



671 



absorb first from the mixture all of the CO 2 by introducing a solution of sodium 

 or potassium hydrate. The reading of the volume left after this absorption 

 is completed compared with the first reading gives the volume of CO 2 . Next, 

 a freshly made alkaline solution of pyrogallic acid is introduced into the tube. 

 This solution absorbs all of the oxygen, whose volume is thus easily determined. 

 The gas that is left unabsorbed after the action of these two solutions is nitro- 

 gen. The volumes of gases are reduced, as is the custom, to unit pressure 

 and temperature, that is, to zero degree centigrade and 760 mms. barometric 

 pressure. A correction must also be made for the tension or pressure exerted 

 by the aqueous vapor in the gases. These corrections are made by means 

 of the following formula: 



V(B-T) 



760 X (I + 0.003665 1) 



in which V 1 represents the corrected volume, V the volume actually observed, 

 B the barometric height at the time and place of the observation, T 

 the aqueous tension at the temperature of the reading, and t the temperature 

 in degrees centigrade. 



Determination of the Oxygen by the Potassium Ferricyanide Method. For 

 the determination of the oxygen in small quantities of blood a convenient 

 method has been introduced by Haldane 

 which is applicable for clinical as well as 

 experimental purposes. The principle of 

 the method consists in first laking the blood 

 with ammonia and then adding a solution 

 of potassium ferricyanide. A reaction en- 

 sues in which oxygen is given off in an 

 amount identical with that obtained by 

 submitting the blood to a vacuum. This 

 method has found its most convenient ap- 

 plication in the Barcroft apparatus (Fig. 

 273), in which the volume of gas liberated 

 is calculated from the pressure change 

 caused in a differential manometer. The 

 manometer (M) is a U-tube, provided above 

 with stopcocks through which communica- 

 tion may be made with the outside air, and 

 connected with two pear-shaped bottles in 

 which the blood to be analyzed is placed. 

 The manometer contains also a central tube 

 (A) through which the two limbs of the 

 manometer may be filled with clove oil to 

 a certain height about half way up the 

 tubes. In making a determination the stop- 

 cocks are left open, and in each of the pear- 

 shaped bottles one places 1 c.c. of blood 

 and 2 c.c. of dilute ammonia. The appa- 

 ratus is thoroughly shaken to lake the 

 blood, and then on one side a little of a 

 saturated solution of potassium ferricyanide 

 is placed in a special receptacle in the stop- 

 per of one of the pear-shaped bottles. The 

 stoppers are inserted, the stopcocks are 

 closed, and then by turning the bottle the 

 ferricyanide is allowed to mix with the 

 blood on its side. Oxygen is given off, and 

 the pressure caused by it is indicated by the difference in level of the clove 

 oil in the two limbs of the [manometer. From this pressure difference the 

 volume of the gas is given by the formula x = k p, in which x is the volume 

 of the oxygen gas in cubic millimeters, p is the pressure difference shown by 

 the manometer, and k is a constant. Before using the apparatus the value 

 of k must be determined experimentally by liberating a known volume of 



Fig. 273. Differential manometer 

 for oxygen determination in blood: 

 M, The manometer containing clove 

 oil; A, the central tube used to fill M 

 with the clove oil. The manometer 

 communicates above with the two 

 pear-shaped flasks in which the speci- 

 mens of blood are placed, and in one 

 of which the oxygen is liberated by the 

 action of the potassium ferricyanide. 

 (See text for description of the method 

 of using.) (Barcroft and Roberta.) 



