382 Drs. Wakelin Barratt and Warrington Yorke. [May 7, 



An example will make this clear. In an experiment upon a rabbit the 

 volume of the mixture was 1*12 c.c., and the proportion of plasma in the 

 mixture determined by the haemocrit 85 - 3 per cent. The proportion, by 

 volume, of plasma in the undiluted blood was therefore 



(S5fxM2-0-20)f = 821 percent 



2. To carry out the second procedure a solution of haemoglobin was 

 prepared, usually by laking the red blood cells of the animal whose blood 

 volume was to be determined, though in some experiments the red blood cells 

 of another animal of the same species were employed instead of the animal's 

 own red cells. To this end the required amount of blood was takeD from a 

 vein, usually by means of a cannula or hollow needle, and added to a sufficient 

 quantity of a 1-per-cent. solution of potassium oxalate to prevent clotting. The 

 mixture was then centrifugalised, the supernatant plasma completely 

 removed, and to the red cells distilled water added in amount just sufficient to 

 produce laking. When this had occurred, solid sodium chloride was added in 

 the amount required to produce a - 85-per-cent. solution of this salt. The red 

 cell constituents which separated out on the addition of sodium chloride, 

 forming a reddish white precipitate, were then separated by centrifugalisation 

 and a dark red solution obtained. The strength of this solution was 

 determined by matching a portion of it, suitably diluted, with a solution 

 containing a known percentage by volume of red blood cells, the solution 

 being prepared by adding a measured amount of oxalated blood, previously 

 submitted to a haemocrit determination, to distilled water. The matching 

 was sometimes carried out in a Zeiss comparison spectroscope, but more 

 frequently we employed the simpler plan of estimating the percentage of 

 haemoglobin in the diluted solution by means of v. Fleischl's haemoglobin- 

 ometer, the scale of which had been previously standardised by means of 

 solutions of haemoglobin representing known percentages by volume of red 

 blood cells. In this way the strength of the haemoglobin solution employed, 

 which usually represented the amount contained in 25 to 40 per cent, of its 

 volume of red cells, is determined. A measured volume of this solution, 

 corresponding to a known volume of red cells, was then injected into a vein 

 of the animal whose blood volume was to be ascertained. As soon as the 

 injection was completed a sample of blood was taken from a vein on the 

 opposite side of the body, added to a known quantity of a 1-per-cent. solution 

 of potassium oxalate, and the volume of the mixture measured. The mixture 

 was then centrifugalised and the percentage of dissolved haemoglobin 

 determined as above described. 



