572 TISSUE RESPIRATION 



tion of the blood gas of the artificially perfused organ in situ, 

 taking samples of the blood from the artery and from the 

 vein for testing. Of course, the amount of blood passing 

 through the organ in a unit of time must be known. 

 Formerly it was customary to make use of Ludwig's 

 stromuhr for this purpose. At present Brodie's method is 

 found an improvement, the organ being enclosed her- 

 metically in a capsule, the vein pinched shut for a measured 

 length of time and the blood at the same time allowed to flow 

 on in the artery; the increase in volume in the organ thus 

 occasioned is measured oncometrically. 



Blood Gas Analysis, Bar croft and Haldane's Method. 

 The methods to be considered for analysis of the gases of the 

 blood in studies of this sort are in part based upon the 

 use of Pfliiger's mercury pump, in part upon the application 

 of Haldane 's method of determining the oxygen in the blood 

 by driving it out of the blood by means of potassium ferri- 

 cyanide after laking. Anyone desiring fuller details of the 

 method may be referred to the excellent paper of Joseph 

 Barcroft, 38 in which the technic of determinations of this 

 sort is set forth with the greatest completeness. As one 

 cubic centimetre of blood is sufficient for the estimation by 

 the Barcroft-Haldane method of gas analysis, it has the 

 advantage of enabling one to work with small organs and to 

 make comparisons of them. The apparatus consists of a 

 small glass receptacle into which by means of a three-way 

 cock the sample of blood to be analysed is introduced directly 

 from the vessel of the animal. The receptacle is so ar- 

 ranged that the oxygen of the sample of blood is set free by 

 potassium ferricyanide, and the increase of pressure thus 

 produced is measured by a manometer. A similar pro- 

 cedure, in which, instead of the ferricyanide, tartaric acid is 

 used, serves for the determination of the carbonic acid by 

 freeing it from its alkaline combinations. The oxygen 



38 J. Barcroft (Cambridge), Ergebn. d. Physiol., 9, 763-794, 1908. 



