BLOOD 



497 



The fact that the CO2 can be completely removed from 

 blood containing the red cells but not from the plasma 

 without the addition of a weak acid seems to show that the 

 haemoglobin acts as an acid. 



(ii.) Haldane and Barcroft have devised a convenient 

 method, which depends upon the fact that the oxygen can 



Fig. 203. — Diagram of one Form of Mercury Pump for Collecting the Gases 

 of the Blood. 21. B., the mercury bulb which can be raised so as to 

 fill G.B. and a-b with mercury, and lowered so as to produce a Torri- 

 cellian vacuum in them, a and h, clamps by which the blood bulbs 

 may be shut off, to be weighed and to receive the blood. G.B., the 

 bulb in which the gases are collected. T., the three-wa}' tap by 

 which the gas bulb G.B. is connected, either with the blood bulb, or 

 with the eudiometer tube, E. B. is the bath of mercurj- in which 

 the tube filled with mercury is set. 



be driven otF from blood treated with dilute ammonia, by 

 the addition of potassium ferricyanide, and that the carbon 

 dioxide is liberated by adding an acid. The amount of gas 

 may be (a) directly measured in a Dupre"s apparatus, or (6) 

 determined by measuring the increased pressure in the tube 

 in which the gas has been given off, by means of Barcroft's 

 apparatus (Chemical Physiology). 

 32 



