ACIDOSIS 45 



shown in Fig. 136, page 395." One c.c. of CCX-free ammonia water is placed in the 

 bottle and the 1 c.c. of plasma delivered beneath it. The bottle is then connected 

 with the manometer with the precautions described elsewhere in this volume. When 

 temperature conditions have been allowed for, saturated tartaric acid is mixed with 

 the plasma solution and the gas evolved measured by the displacement of the fluid 

 in the manometer. The apparatus may also be used with blood in place of plasma. 

 In this case, however, it is necessary that the oxygen be removed before adding the 

 tartaric acid. This precaution is necessary, since acid can dislodge some of the H, from 

 hemoglobin. The blood is therefore first of all laked with ammonia containing some 

 saponin, then shaken with 0.25 c.c. saturated potassium ferricyanide solution, and 

 finally with the saturated acid solution. If blood is used, the estimations must be 

 made on strictly fresh blood, since on standing the CO 2 combining power greatly de- 

 teriorates. 



From what has been said in the introductory part of this chapter it is 

 clear that the plasma furnishes only the first line of defense of the body 

 against excess of acid; the corpuscles form the second line of defense, so 

 that a truer estimate of the * ' reserve alkalinity ' ' is afforded when the C0 2 - 

 combining power of whole blood rather than that of plasma is used. The 

 reason why Van Slyke recommends the latter is because the estimations 

 are much easier, there being no hemoglobin to complicate the process, and 

 there can be no doubt that his method has been of immense value in the 

 elucidation of the acidosis problem, and that for the majority of diagnos- 

 tic purposes it is perfectly satisfactory. For further advancement of 

 knowledge it is advisable, however, to use the whole blood as has been 

 done by Christiansen, Haldane and Douglas, 22 and by Morawitz and 

 Walker, 23 and more recently by Haggard and Henderson 21 . 



Another question remains to be considered, namely, whether arterial or 

 venous blood should l>e employed. For various reasons arterial blood is 

 preferable. In the first place the percentage of C0 2 actually present in it 

 is proportionate to the alkaline reserve, because the respiratory center is 

 so sensitive to the slightest excess of this acid (see page 353) that it stimu- 

 lates respiration so as to remove the excess and thus maintain the C0 2 of 

 the arterial blood at exactly the point which corresponds to its alkaline 

 reserve. It is, therefore, unnecessary to expose the blood to an atmosphere 



*This form of Haldane-Barcroft apparatus is not quite the same as the differential manometer 

 that is used for measurement of the Oa-combining power of hemoglobin (page 395). In the form 

 used for the present purpose, a side tube at the bend of the U-tube is connected with a small rub- 

 ber bag, which can be compressed by a screw. When the gas is evolved in the bottle, it presses 

 down the fluid in the proximal limb of the manometer correspondingly and raises that in the distal 

 limb. Since the calculation of the amount of gas evolved depends on finding the pressure produced 

 without any change in volume, it is necessary after the gas has been evolved to compress the rubber 

 bag until the meniscus of fluid in the proximal limb of the manometer is brought back to its original 

 level. The height at which the fluid stands in the distal limb then obviously corresponds to the 

 pressure created by the evolved gas. 



The equation for determining the amount of gas evolved depends on the gas law, which states 

 that the pressure of a gas is inversely proportional to its volume (page 353). Suppose that the 

 volume of gas evolved was equal to the volume of the bottle, then, since the volume has been 

 kept constant, the pressure would be doubled that is, the fluid in the distal limb would equal that 

 of 1 atmosphere, or 10,400 mm. of water or 10,000 of clove oil, which is the fluid actually used to 

 fill the manometer. Any other observed pressure would therefore correspond to the volume of 

 evolved gas according to the equation, 



... vol. of bottle (and tubing to meniscus) 



V = nnn :- ^ X mm. Pressure m Manometer. 



10,000 (when clove oil is used) 



In using the apparatus in the above manner, only one of the bottles is employed, and the tartaric 

 acid is added from a pocket in the stopper by a simple manipulation. 



