1178 PHYSIOLOGY 



To determine A. The centre tube x is marked in one-hundredths of a 

 cubic centimetre. Expel 0-1 c.c. from it into the manometer tubes, which are 

 of the same size. 0-05 c.c. will have gone into each ; read the difference in level. 

 From the mean of a number of such readings A is directly deducible. 



To determine v. With a knowledge of A, v may be obtained by an application 

 of Boyle's law. Fill the bottles almost full of water, putting, say, 25 c.c. of water 

 in each, shut one of the taps, keeping the other open. Tighten the screw so as 

 to produce a known compression on the closed side ; observe the difference of 

 pressure produced. The tubes should be moistened with oil before the experiment 

 commences. 



To 'determine the oxygen capacity of a sample of blood. Place 2 c.c. of ammonia 

 solution (made by adding 4 c.c. of strong NH 3 to a litre of water) in one of the 

 bottles and add 1 c.c. of blood. Thoroughly lake the blood. Put vaseline on the 

 large and small stoppers. Put 0-2 c.c. of a saturated solution of potassium 

 ferricyanide in the small tube contained in the stopper of the bottle containing 

 the blood (this is best done with a fine pipette which goes down these tubes). 

 Put in the small stopper. Place the apparatus on the side of a large water bath 

 (such as a pail) with both taps open. In about five minutes close the tap on the 

 side of the blood and rotate the bottle on the stopper till the ferricyanide trickles 

 into the laked blood. Shake thoroughly, replace in the bath, and repeat this 

 several times till a constant difference of level is obtained. By means of the screw 

 clamp bring the column of oil on the side of the blood to its original level, and then 

 measure the difference of level between the two sides. Let this difference of 

 level be y mm. ; let p be the height of the barometer in millimetres of clove oil, 



and x the volume of oxygen given off in cubic millimetres ; then x y ( ! 



Except in the most exact work p may be taken as 10,000 mm., in which case the 



V 



expression maybe determined once for all and called C, the constant of the 



apparatus : then x = y x C. 



To determine the gaseous contents of a given blood. If we wish to determine 

 the actual amount of oxygen as oxyhaemoglobin in the sample, the blood must be 

 carefully introduced so as to lie below the ammonia and not to come in contact 

 with the air. The stopper is then replaced in the bottle and immersed in the 

 bath, with both taps open until it has attained a constant temperature. The tap 

 is then closed and the height of the column of- oil noted. The blood is then 

 laked by rotating the apparatus, and after allowing five minutes for complete 

 laking the ferricyanide is run in. The rest of the determination is carried out as 

 above. 



The carbon dioxide may be determined in the same sample of blood by running 

 in tartaric acid in the same way as potassium ferricyanide was previously run in. 

 It is necessary always to determine the oxygen before the carbon dioxide, since 

 the mere 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. 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 



