THE CHEMISTRY OF RESPIRATION 



499 



chemical agents. The usual procedure then is to expose the blood at 

 body-temperature to as perfect a vacuum as can be obtained, but it 

 must have been defibrinated or must have been rendered non-coagu- 

 lable by the addition of an oxalate or citrate solution. 



The Torricellian vacuum was first employed for the extraction of the gases of 

 the blood by Ludwig and Setschenow. 1 Air-pumps of simple construction have 

 been described by Pfliiger 2 and Grehant 3 (Fig. 255) and one of greater complexity 

 by Topler-Hagen. The latter has been modified by Zuntz and Barcroft. 4 It 

 consists of a Woulfe bottle (A) filled with mercury and a long capillary tube which 

 also contains mercury (Fig. 256). Bottle A is connected with the water supply 



FIG. 256. BABCKOFT'S MODIFICATION OP THE TOPLER PUMP. 



tube by two taps W. The vacuum (B) is shut off against the sulphuric acid cham- 

 ber (E) for drying the gases by a glassfloat (Y). At F a condenser is interposed 

 through which a stream of cold water is kept flowing. The blood is led from the 

 cylinder K into the receptacle G as soon as a vacuum has been established. This 

 end is accomplished by permitting water to flow through the tap W into the Woulfe 

 bottle A. The mercury is then forced into tube B, where its further progress 

 toward E is finally made impossible by the raising of the glass valve Y. Its 

 only exit now is through C into D. If the influx of water is now made to cease, and 

 the second tap W is opened, the mercury assumes its original position. If the air 

 is at this time prevented from entering at D, the valve Y drops downward and per- 



1 Ber. der Akad. der Wissensch., Wien, 1859. 



2 Unters. aus dem physiol. Institut zu Bonn, 1866. 



3 Compt. rend., Ixxv, 1872. 



4 Ergebn. der Physiol., vii, 1908, 699. 



