78 HEMOGLOBIN 



quite convinced me that these apparently anomalous results were 

 the opening of a new chapter with regard to the osmotic pressure of 

 haemoglobin. 



It need hardly be said that the problem bristles with difficulties. 

 Had it not done so I doubt if it would have thrown its spell over 

 Adair (8), (9), who has carried out the most recent and the most 

 complete work in this field. Perhaps before discussing Adair's work 

 a word or two might be said about these difficulties. They fall into 

 several categories, the first of which is that of the actual measure- 

 ments. These measurements are two, that of the concentration of 

 the solution and that of the height to which it rises in the osmometer. 

 It is not easy to measure the concentration of a haemoglobin solution. 

 Reid, and later, Hiif ner, used the spectrophotometer for this purpose ; 

 their method is now probably of historical interest and may be found 

 in a chapter by Gamgee in Schafer's (lO) text-book. Stoddard and 

 Adair (11) applied a method based on measurements of the re- 

 fractive index. This method had previously been used to measure 

 the concentrations of other proteins. It was duly checked by chemical 

 analysis. 



The question may, however, be asked: Why nqt take the oxygen 

 capacity as a measure of the concentration of haemoglobin ? A trifling 

 doubt in the quantity of oxygen which unites with each gram of 

 haemoglobin is not very material if the point at issue is whether 

 the osmotic pressure is in the end going to correspond to Hb or Hb^ . 

 There are some other considerations, however. Account must be 

 taken of that ill-understood form of haemoglobin which does not part 

 with its oxygen either in the f erricyanide or in the Van Slyke apparatus. 

 Moreover, reliable oxygen readings can only be obtained from haemo- 

 globin solutions of considerable concentration; a part of the merit 

 of Adair's work is that it deals with dilute, as well as strong solutions. 

 The difficulty of measuring the concentration, then, is the first which 

 has to be overcome in the estimation of the osmotic pressure of 

 haemoglobin. As in all such matters the position cannot really be 

 regarded as satisfactory until two independent methods give results 

 which agree. Till then we must take our choice and as between the 

 spectrophotometer and the refractometer, the latter would seem to 

 be the more desirable. 



Now let us pass to the second difficulty of actual measurement — 

 that of obtaining a reliable reading for the pressure itself. Here one 

 is on the horns of a dilemma. If you do not keep your solutions long 



