126 EXPERIMENTAL PHYSIOLOGY. 



For this purpose the piston is cautiously pushed up, with E and B 

 in communication, until mercury stands at the zero mark on the 

 neck of the gas burette. The clip (4) is then screwed down and 

 the levelling burette (G) lowered until the menisci stand at the 

 same level in it and the burette. This brings the gas to atmospheric 

 pressure and the volume is read and noted. The reading gives the 

 C.C. of gas in 10 c.c. blood. The volume should be reduced to 

 standard temperature and pressure (for calculation see Exp. 50). 

 To analyze the gas a 40 per cent, solution of sodium hydroxide is 

 sucked from a watch glass into a 2 c.c. all-glass syringe, and the 

 tube of the syringe inserted in the side tube (H). All air must be 

 expelled from this tube. With the pinchcock (6) closed, the clip 

 (5) is opened, while gentle pressure is being maintained on the 

 piston of the small syringe so that the mercury may not run into 

 it. The NaOH runs up to the top of the mercury column (F), and 

 when it is all in, clip 5 is again screwed down. The syringe (I) is 

 removed and F inverted several times so that the carbon dioxide 

 in the gas contained in it may be thoroughly absorbed. On now 

 opening clip 6, the mercury will rise in F, and by adjusting the 

 levelling tube the shrinkage in volume due to the absorption of 

 CC>2 can be ascertained and the percentage of this gas determined. 

 The reading is taken which corresponds to the top of the NaOH 

 solution, a similar amount of NaOH solution being placed on the 

 *.op of the mercury in the levelling tube. Care must be taken to 

 see that all the CO2 is absorbed. 



To absorb the oxygen, about a gram of pyrogallic acid is dis- 

 solved in 2 c.c. of water in the watch glass, the solution is introduced 

 into jP. and the further manipulations conducted in the same 

 manner as for the NaOH solution. The gas which remains when 

 both CO2 and O2 are absorbed is nitrogen. There should not be 

 more than 0.1-0.2 c.c., any larger amount being due to air leakage 

 into the apparatus during the manipulations.* By taking proper 

 precautions, however, the residual nitrogen should never be more 

 than 0.3-0.5 c.c. The results are to be calculated to give the amounts 

 of each gas in 100 c.c. of blood. 



*If any considerable amount of nitrogen is left, its volume should be measured, 

 and after subtracting C>2, the volume of C>2 that must have been introduced, as 

 air, calculated and subtracted from the actually observed O 2 . 



