970 PHYSIOLOGY 



ferricyanide are then poured into the small tube B (the length of which should 

 slightly exceed the width of the bottle) and placed upright in A. The rubber 

 stopper, which is provided, as shown, with a bent glass tube connected with the 

 burette by stout rubber tubing of about 1 mm. bore, is then firmly put in, and 

 the bottle placed in the vessel of water c, the temperature of which should be as 

 nearly as possible that of the room and of the blood and water in the bottle. If 

 the stopper is not heavy enough to sink the bottle the latter should be weighted. 

 By opening to the outside the three-way tap (or T-tube and clip) on the burette, 

 and raising the levelling tube, which is held by a spring clamp, the water in the 

 burette is brought to a level close to the top. The tap is then closed to the 

 outside, and the reading of the burette (which is graduated to -05 c.c., and may 

 be read to -01 c.c.) taken after careful levelling. 



The water-gauge (which has a bore of about 1 mm.) attached to the tempera- 

 ture and pressure-control tube is now accurately adjusted to a definite mark. 

 This is easily accomplished by sliding the rubber tube backwards or forwards 

 on the piece of glass tubing D. The control tube is an ordinary test-tube 

 containing some mercury to sink it, and connected with the gauge by stout 

 rubber tubing of about 1 mm. bore. 



As soon as the reading of the burette is constant, which it will probably be 

 within two or three minutes, the bottle is tilted so as to upset B, and is shaken as 

 long as gas is evolved. During this operation B should be repeatedly emptied, 

 as otherwise the oxygen dissolved in its liquid might not be completely given 

 off. When the evolution of oxygen has ceased the bottle is replaced in the 

 water. If, as is probable, the pressure-gauge indicates an alteration in the 

 temperature of the water, cold water from the tap, or warmed water, is added 

 till the original temperature has been re-established, and the reading of the 

 burette noted as soon as it is constant. The bottle is again shaken, &c., until 

 a constant result is obtained, for which about fifteen minutes from the beginning of 

 the operations are required. The temperature of the water in the jacket of the 

 burette, and the reading of the barometer, are now taken, and the gas evolved 

 is reduced to its dry volume at and 760 mm. To calculate the oxygen evolved 

 from 100 c.c. of blood, allowance must be made for the fact that a 20 c.c. pipette 

 does not deliver 20 c.c. of blood, but only about 19-6 c.c. The actual amount 

 of shortage for a given pipette can easily be determined by weighing the pipette 

 after water, and again after blood, has been delivered from it. A further slight 

 correction is necessary on account of the fact that the air in the bottle at the end 

 of the operation is richer in oxygen than at the beginning, so that, as oxygen is 

 about twice as soluble as nitrogen, slightly more gas will be in solution. With 

 a bottle of 120 c.c. capacity, and 20 per cent, of oxygen in the blood, the air in 

 the bottle at the end will evidently contain about 27 per cent, of oxygen, so that, 

 assuming that the coefficients of absorption of oxygen and nitrogen in the 54 c.c. 

 of liquid within the bottle are nearly the same as in water, the correction will 

 amount at 15 C- to -06 c.c. in the reading of the burette, or + 0-30 per cent, in 

 the result." 



THE SPECIFIC GRAVITY OF THE BLOOD 



The specific gravity of the blood may be determined by directly 

 weighing a sample, or more conveniently by collecting blood in a 

 capillary tube and discharging drops of it into a series of vessels con- 

 taining glycerin and water mixed in varying proportions. When it 

 is found that the drop of blood as it leaves the capillary vessel neither 

 rises nor falls in the glycerin and water mixture, we know that the 

 specific gravity of the blood is identical with that of the mixture. A 



