THE CHEMISTRY OF RESPIRATION 1055 



One of the best modifications of the Topler mercury pump is that employed 

 by Barcroft (Fig. 493), which differs little from the pump devised by Bohr. 



The construction of the pump is shown in the diagram. The actual pump consists 

 of the parts A, B, c, D. The bulb B is prolonged below by a wide tube dipping into the 

 mercury in the Woulf bottle A. The upper part of the bottle is filled with water and 

 connected by two taps at w with the water-supply and with a sink. The water being 

 turned on, mercury is forced up into B ; as it rises into Y it carries before it a glass valve 

 which prevents its further passage, so that it can only escape by the tube c, driving 

 before it all the air previously contained in B. The water-supply is now turned off, and 

 the tap to the sink turned on. The mercury runs back. Air cannot enter by c, since 

 this tube is sealed by mercury. The valve Y therefore sinks and allows the air in the 

 blood receivers G, G and the rest of the apparatus to escape into B. The process is re- 

 peated many times until a high vacuum is produced in the whole apparatus. A measured 

 quantity of blood is now let into the lower bulb G. F is a condenser through which cold 

 water is constantly flowing (to prevent all the blood boiling away), while warm water 

 circulates round the bulbs G, G to facilitate the giving off of the blood gases. The blood 

 boils in the vacuum, and the gases escape into B, and may be driven off and collected 

 over mercury in a cylinder D by raising the mercury in B. The process of exhaustion is 

 repeated until no more bubbles rise into D on filling the bulb B with mercury. E is a 

 sulphuric acid chamber for drying the gases as they pass from the blood to the bulb B. 



In this way, from 100 c.c. of blood, about 60 c.c. of mixed gases may be 

 obtained, consisting of oxygen, carbon dioxide, nitrogen, and argon. Argon 

 is present only in insignificant quantities, about -04 volume per cent. The 

 nitrogen also forms only between one and two volumes per cent, and is 

 present in the same proportion in both arterial and venous blood. The 

 amounts of oxygen and carbon dioxide in these two kinds of blood differ, 

 however, within wide limits. The following Table represents the average 

 composition of the gases obtained from an artery and a vein of the dog : 



From 100 vols. May be obtained 



Of oxygen Of carbon dioxide Of nitrogen 



Of arterial blood . .20 vols. . 40 vols. . 1 to 2 vols. 

 Of venous blood . 8 to 12 vols. . 46 . 



Measured at 760 mm. and C. 



The principle introduced by Haldane (vide p. 859) for the determination of the 

 oxygen combined in the form of oxyhaemoglobin may be successfully applied to small 

 quantities of blood, such as 1 c.c. or even 0-lc.c., and in the same sample of blood the 

 carbon dioxide may also be determined. In this way it becomes practicable to make 

 blood-gas analyses in a patient, or in experiments on small organs where it is desired 

 to determine their gaseous metabolism by comparing the arterial with the venous 

 blood. Barcroft's apparatus for dealing with 1 c.c. of blood is shown in Fig. 494 A. 



The apparatus consists of two bottles of identical size (about 30 c.c.) attached to a 

 manometer, the tubing of which is 1 mm. bore. The manometer is filled with clove oil 

 of known specific gravity. To fill it take out the centre tube, put in clove oil at A, put 

 in the centre tube with the glass tube B open and some pressure on the rubber tube c. 

 The oil should stand about half way up each tube ; seal B in a flame. The constant 

 of the apparatus must be determined, viz. the capacity of the bottles and with their 

 connections. 



It is determined by finding what rise of pressure in the apparatus is produced by 

 the liberation of a known volume of oxygen from hydrogen peroxide, which is placed in 

 the bottle, the liberation being effected by the addition of potassium. 



