QUANTITY AND COMPOSITION OF THE BLOOD IN MAN 903 



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 temperature 

 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 rnm. 

 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, etc., 

 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 lair 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 -f- 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 containing glycerin and water mixed in varying pro- 

 portions. 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 graduated series of these mixtures is kept in bottles 

 and their specific gravity is generally determined before the experiment. 

 Hammerschlag's method consists in placing a drop of blood in a mixture 

 of chloroform and benzene and then adding chloroform or benzene, as 

 the case may be, until the drop neither rises nor falls. The specific 

 gravity of the mixture is then taken. The specific gravity varies in man 

 between 1057 and 1066, and in woman from 1054 to 1061. It is increased 

 by loss of water, as after profuse perspiration, or by passive congestion 



