BY DR. BURDON-SANDERSON. 205 



contains, whether free or combined, escapes from it, its place 

 being taken by carbonic oxide. The blood-coloring matter in 

 combination with this gas acquires optical and other characters 

 which remarkably resemble those of oxyhjjemoglobin. 



5. Carbonic acid gas may be extracted from arterial blood 

 by the Torricellian vacuum in the proportion of about 35 vol- 

 umes (as estimated at 760 millimetres pressure and tempe- 

 rature) to 100 volumes of blood. Venous blood may yield 43 

 volumes, asphyxial blood 50 volumes. Of this quantity a cer- 

 tain but very varying proportion is merely absorbed, the rest 

 is in loose combination, principally with the sodic carbonates 

 of the plasma. It is probable that some of it is held by the 

 bibasic sodic phosphate of the blood, and perhaps some other- 

 wise. Hence it may be readily understood that serum con- 

 tains as much carbonic acid gas as a corresponding volume of 

 blood. 



6. When a fixed acid, e. g., tartaric acid, is added in vacuo to 

 blood which has been already deprived of its absorbed and 

 loosely combined carbonic acid (which together constitute 

 what may be called its inexhaustible carbonic acid), an addi- 

 tional quantity of carbonic acid may be obtained from it, which 

 previously existed in the blood in the condition of neutral car- 

 bonate, principally if not entirely sodic. 



Every apparatus for extracting the gases of the blood must 

 consist of two parts, a mercurial pump and a recipient. The 

 form and character of the latter necessarily depend upon those 

 of the former. The most important forms of pump in use are 

 those of Dr. Geissler, and others similar, employed in Ger- 

 many, and of M. Alvergniatj in Paris. In this country, under 

 the direction of Professor Frankland, Mr. Cetti has constructed 

 a Sprengel's pump for the purposes of extracting the gases of 

 water. Dr. Gam gee, of Edinburgh, has applied this form of 

 pump to the extraction of the gases of the blood with complete 

 success. 



26. Alvergniat's Pump. A long barometer tube, the 

 scale of which is divided into millimetres, is fixed to a vertical 

 board on a suitable stand. This tube is dilated at the top into a 

 large bulb (a, Fig. 197), and is then continued upwards until it 

 ends in a three-way stopcock (c/), surmounted by a funnel. To 

 the right, the stopcock is in communication with a glass tube, 

 ending in a bulb (</), and possessing a flexible joint at/. To 

 the lower end of the barometer tube is fitted a long tube of 

 thick-walled vulcanized caoutchouc, which ends in a globular 

 mercury-holder (u). The vertical board is fitted at regular in- 

 tervals with perforated shelves, on one of which the mercury- 

 holder is resting. The pump is worked as follows: v having 

 been filled with mercury, the metal enters the vulcanite tube, 

 and rises to the same height in the tube a c as in v. If v is 



