24 HAEMOGLOBIN 



or ammonia, may be demonstrated in the following way. The position 

 of maximum density of the principal band in the spectrum of 

 ammonia haemochromogen is 35 Angstrom units nearer the blue end 

 than that of the corresponding band of globin haemochromogen. If 

 two vessels are placed in the beam of light of a Hartridge reversion 

 spectroscope, one containing ammonia haemochromogen and the other 

 containing globin haemochromogen, the band will appear to be in a 

 position intermediate between those of the pure ammonia and the 

 pure globin compounds. The exact position depends upon the relative 

 concentration of the two compounds. Thus if the concentration of the 

 globin compound be increased the band shifts towards the red, if 

 the concentration of the ammonia compound be increased the band 

 shifts towards the blue. Start then with the combined band in a 

 certain definite position and add reduced haematin to the solution 

 which contains the ammonia haemochromogen. The band at once 

 shifts towards the violet showing that the concentration of ammonia 

 haemochromogen in the fluid has increased. In a solution of haemo- 

 chromogen what proportion does the concentration of haemochromogen 

 bear to those of the reduced haematin and the globin which are 

 present? The precise answer is not known. The combination is almost 

 complete, the concentrations of haematin and globin being very small 

 relatively to the concentration of haemochromogen. When the whole 

 range of haemochromogens is reviewed the fact emerges that globin 

 haemochromogen is an exception in this respect. Contrast it with 

 ammonia haemochromogen. To obtain that substance it is necessary 

 to add an overwhelming amount of ammonia to the reduced haematin. 

 So far, indeed, out of all the nitrogenous compounds which have been 

 found to unite with reduced haematin two only have affinities for it, 

 at all approaching that of globin. The two are pjrridine and nicotine. 

 Globin, then, among the nitrogenous compounds which could unite 

 with haematin, has a very special place, if only because it is one of 

 the few substances which have a great affinity for haematin. 



Haematin is a very insoluble substance, and a second respect in 

 which globin presents an especial interest is that it forms a vehicle 

 for the conversion of the insoluble haematin into a soluble compound. 



Let us now pass to the consideration of the nature of haemoglobin 

 in the light of what we know of haemochromogen. What is the relation 

 of the one to the other? Several workers have claimed the distinction 

 of having prepared haemoglobin; they may have done so but until 

 recently there has been great difficulty in repeating these prepara- 



