Tributes 



consuming, and required large volumes of blood. Barcroft utilized the 

 ferricyanide reaction, which had just been studied quantitatively by 

 J. S. Haldane, to determine the oxygen capacity of blood samples, and 

 he designed apparatus for blood gas analysis which required only small 

 volumes of blood, dispensing with the elaborate vacuum pumps which 

 had previously been necessary. For work on the dissociation curve, 

 his differential manometer was the most elegant, and could be adapted 

 for volumes of blood as small as a tenth of a cubic centimetre. This 

 manometer has been very extensively used in many types of research, 

 and is familiar to almost all biochemists. 



With the differential apparatus it was possible to determine a fair 

 number of points on the dissociation curve in a single day, a factor of 

 great importance, since the oxygen capacity of blood and the properties 

 of haemoglobin undergo changes with time. 



In addition, he designed an apparatus for the equilibration of blood 

 with gas mixtures. This is usually known as the Barcroft tonometer, 

 and is essentially the same as that in general use at the present time. 

 In this apparatus a small volume of blood was exposed in a thin film 

 to a relatively large volume of gas, and equilibrium was reached 

 with greater speed and certainty that had been possible with earlier 

 methods. 



To quote Barcroft's own words, when describing his early work with 

 Camis : ' Our very early efforts seemed to augur speedy success in the 

 construction of a uniform dissociation curve for the blood of various 

 animals. When we came to the blood of man, however, we could 

 never make the dissociation curve agree with that of the cat or rabbit. 

 It was clear then that we had found our way into the morass in which 

 our predecessors had floundered so hopelessly and our newer and 

 more certain methods instead of saving us from their embarrassments 

 only made the uncertainty of our position more certain.' Believing 

 that experimental conditions would thereby be simplified, Barcroft 

 decided to work with haemoglobin solutions instead of with whole 

 blood, but he found more variable dissociation curves with haemoglobin 

 than with blood. To obtain concentrated solutions of haemoglobin 

 they had found it advisable to add ammonium carbonate, but on one 

 occasion, whether by accident or design he could not remember, the 

 ammonium carbonate was omitted. The curve obtained was unlike 

 those determined in the presence of the salt and was reminiscent of 

 curves which had previously been described by Bohr. This experiment 

 suggested that the form of the curve was influenced by the salts present, 

 and Barcroft therefore determined dissociation curves of haemoglobin 

 dissolved in a salt solution based on an analysis of human red blood cor- 

 puscles, and, as he stated in his book : ' Great was our excitement and 



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