410 RESPIRATION 



sources of error connected with the use of a vacuum pump, or necessitates 

 analysis of the gas obtained from the blood. 



Until recently we have used at Oxford the Brodie modification of the 

 Barcroft-Haldane apparatus. As, however, the range of error with this 

 apparatus has been about 2 per cent, I have quite recently devised a 

 new apparatus, with a view especially to more accurate determinations 

 of the oxygen in human arterial blood, and of dissociation curves. ^2 

 With this apparatus it is possible to reach an accuracy as great as with 

 the original ferricyanide apparatus — i.e., to within 0.5 per cent of the 

 oxygen capacity of the blood. This new apparatus will therefore be de- 

 scribed in full. On account of the present difficulty and expense in getting 

 glass apparatus made, it was designed so that it could if necessary be 

 put together in a laboratory from easily obtainable parts, just as in the 

 case of the original apparatus. 



When blood from a blood vessel is used, a glass syringe with solid 

 glass piston is employed for obtaining the sample. This method was first 

 applied to human arteries by Hiirter, and developed by Stadie and others. 

 Professor Meakins, with whom I have been associated in work on human 

 blood gases, employs the following procedure. A very small quantity of 

 finely powdered potassium oxalate is introduced into the bottom of the 

 syringe. The piston is then introduced and a little liquid paraffin drawn 

 in, and as much as possible expelled again with the syringe pointing 

 upwards so as not to expel the oxalate. After disinfection of the skin the 

 needle (previously sterilized) is introduced into the radial artery or other 

 vessel, and about 5 cc. or more of blood withdrawn, a compress and 

 bandage being afterwards applied over the place for an hour if the 

 vessel was an artery. The needle is then removed and washed, and the 

 blood transferred (with the syringe pointing upwards) through a rubber 

 connection into a graduated pipette holding more than 2 cc. From this 

 pipette an exactly measured quantity of about 2 cc. is introduced beneath 

 the sodium carbonate or ammonia solution in the blood-gas flask. At the 

 end of the operation about 0.5 cc. remains in the pipette, so that none 

 of the blood has come in contact with air. 



The apparatus is shown in Figure 103. In principle it is similar to that 

 shown in Figure loi, but designed for small quantities of blood and for 

 determining COg. The blood is received in one of the small flasks shown, 

 while the other is for temperature control. Each has a capacity of about 

 20 cc. The procedure differs according as it is desired to determine the 

 oxygen or the CO2 of the blood. In the former case the first step is to 

 measure 2 cc. of a i per cent solution of dried sodium carbonate into 

 one of the two small flasks (about 20 cc. capacity) shown and add a 



" Haldane, Journ. of Pathol, and BacterioL, XXIII, p. 443, 1920. 



