42 PHYSICAL CHEMISTRY 



gen while it is immersed in the fluid to be investigated, special 

 vessels are necessary, but these are usually inseparably connected 

 with the electrode and included under the term. 



Blood requires more precautions than any other biological 

 fluid when investigated with the hydrogen electrode. When suc- 

 cess has been achieved with it, the same technique and apparatus 

 will serve for any other biological fluid with slight omissions and 

 modifications for expediency. Though many forms of electrodes 

 have been described, but four points in the technique need be 

 emphasized : First, reduce the layer of blood over the platinum 

 as much as possible so that hydrogen can get to the platinum 

 (Michaelis "Wasserstoffionenkonzentration," 1914). Second, 

 shake the hydrogen with another sample of the same blood before 

 passing it into the electrode, otherwise C0 2 will pass from the 

 blood into the hydrogen and leave the blood more alkaline (Has- 

 selbalch, 1913). Third (not absolutely necessary), remove the ery- 

 throcytes. Otherwise the oxygen they contain will combine with 

 the hydrogen in the platinum and reduce its concentration (Mil- 

 roy, 1914). Fourth, connect the apparatus so that the blood is 

 never exposed to the air and CO, lost (McClendon 1916 a). 



Fig. 12. Hollow needle for drawing blood (from JBC). 



% J r* 



Fig. 13. Tube for collecting, defibrinating and centrifuging blood with- 

 out exposure to air. The ends are fitted with rubber tubes (from MRR). 



The following apparatus is the first to include all of these points 

 (McClendon & Magoon, 19 16). 



The blood is drawn through a hollow needle, Fig. 12, connected 

 by rubber tubing to the 10 cc defibrination tube, Fig. 13, and 

 defibrinated with the lead ball with the exclusion of air. This 

 tube is then placed in the centrifuge and the corpuscles precipi- 

 tated. The lower end is connected to a mercury tube and funnel, 

 with the exclusion of air, and the upper end is connected to the 

 Fresenius cock a of the electrode, Fig. 14, that has already been 

 rinsed with distilled water and filled with pure hydrogen. Rais- 



