70 RESPIRATION 



The investigation was now taken up by Barcroft and his pupils, 

 who have made a number of important advances during the last 

 few years with the help of one form or another of the ferricyanide 

 apparatus. 18 



They found that the form taken by the dissociation curve of 

 oxyhaemoglobin is greatly influenced by the salts present in the 

 red blood corpuscles, or in a solution of their oxyhaemoglobin. 19 

 When all the salts were removed by dialysis the curve became a 

 rectangular hyperbola, 20 as in the curve published by Htifner. If 

 the reversible reaction between oxygen and haemoglobin is rep- 

 resented by the uncomplicated equation Hb + O 2 *^HbO 2 , the 

 curve would, in accordance with the well-known law of Guldberg 

 and Waage, be a rectangular hyperbola. This is the case when 

 salts are absent and the solution is neutral, as in the dialysed solu- 

 tion. When, however, salts are present, the form of the curve is 

 altered towards the characteristic form given by blood, and the 

 nature and extent of the alteration was found to depend on the 

 nature and concentration of the salts. Thus when dialysed dogs' 

 haemoglobin was dissolved in a salt solution of the same composi- 

 tion and concentration as in human blood corpuscles the dissocia- 

 tion curve obtained was similar to that of human blood. 



These discoveries rendered it unnecessary to assume with Bohr 

 and others that there is any essential chemical difference between 

 the haemoglobin present in blood corpuscles and in a solution of 

 crystallized haemoglobin. At the same time they furnished a key 

 to the explanation of the apparently divergent observations as to 

 the dissociation curve of oxyhaemoglobin. Barcroft and Orbeli 21 

 found that not only does CO 2 shift the curve in the direction dis- 

 covered by Bohr and his pupils, but that other acids added in 

 such small quantities as not to decompose the haemoglobin have a 

 similar effect, while alkalies have the opposite effect. As will be 

 explained later Barcroft and his associates concluded that this 

 alteration affords a very sensitive measure of any alteration in the 

 reaction, or hydrogen ion concentration of the blood; and they 

 have used it for this purpose. 



The form of the dissociation curve of the oxyhaemoglobin in 

 human blood at body temperature and with a constant pressure of 



18 A summary of these investigations is given in Barcroft's book, The Respira- 

 tory Function of the Blood, 1914. 



19 Barcroft and Camis, Journ. of Physiol., XXXIX, p. 118, 1909. 



20 Barcroft and Roberts, Ibid,., XXXIX, p. 143, 1909. 



21 Barcroft and Orbeli, Journ. of Physiol., XLI, p. 353, 1910. Barcroft, Ibid., 

 XLII, p. 44, 191 1. 



