44 



PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



The same procedure is repeated with 1 c.c. water, so as to wash in all of the plasma/ 

 arid finally 0.5 c.c. of 5 per cent H SO is sucked in, after which stopcock I is turned 

 off. The reservoir F is then lowered sufficiently to allow all of the mercury, but none 

 of the blood, to run out of B and C. A vacuum is thus produced in B and C. 



As the level of the mercury falls in B and C, the plasma effervesces violently,* be- 

 cause it is exposed to a vacuum. To be certain that all traces of CO have been 

 dislodged from the solution, the apparatus is inverted several times. To ascertain how 

 much CO 2 has been liberated, stopcock II is now turned so as to bring C and E into 

 communication, and by cautiously lowering the reservoir the fluid in C is allowed to 

 run into the bulb E. Stopcock II is thereafter turned so as to connect C and D, and 

 the reservoir raised so that the mercury runs into C as far as the CO that has col- 



Fig. 11. Van Slyke's apparatus for measuring the CDs-combining power of blood in blood plasma. 

 For description, see context. 



lected in the burette will permit it to go. After bringing the level of the mercury 

 ir. F to correspond to that in the burette, the graduation at which this stands is read. 

 It gives the c.c. of CO liberated from the plasma. Under the above conditions normal 

 plasma binds about 75 per cent of its volume of CO 2 ; therefore, since the total capacity 

 of the pipette is 50 c.c., the mercury should stand at 0.375 c.e. on the burette. For 

 accurate measurement it is necessary to allow for the CO 2 that remains dissolved in 

 the water, etc., as well as for barometric pressure and temperature. This is best done 

 by the use of a table based on the known solubility of CO., under the various condi- 

 tions obtaining, which is given in 'van Slyke's paper. 12 



*This may be prevented by adding a small drop of caprylic alcohol. 



