228 HAEMOGLOBIN. 



remain very constant, the increase in the amount of oxyhaemoglobin 

 influencing more the intensity of the band than its width. In the case 

 of solutions containing approximately the proportion of oxyh?emoglobin 

 above mentioned (i.e. from 0*20 to - 33 parts in 1000), the spectral 

 region between F and G is absolutely unshaded. Soret's band is then 

 seen, extending from X 404 X 434 ; i.e. it occupies the greater part of the 

 spectral region intervening between G and H ; the edges, however, 

 uniformly shade away as far as these lines. 



By examining a series of photographs of spectra obtained by inter- 

 posing solutions of oxyhsemoglobin of very different concentrations, I 

 have determined that the mean ray absorbed does not, as Soret thought, 

 coincide with h (x 410*1), but is decidedly on the red side of that line, 

 corresponding to X 414. 



When the concentration of the solution of oxyhsemoglobin increases, 

 the width of the band very slowly increases. Its less refrangible border 

 never passes beyond G ; as the solution becomes highly concentrated, 

 the band widens perceptibly, and it does so in the direction of the ultra- 

 violet. With a solution made by diluting 1 volume of blood to the volume 

 of 250 (water or O'l per cent, solution of Na(OH) being employed as the 

 diluent), the absorption-band, though much more intense than with the 

 more dilute solutions, retains almost the same boundaries, its shadowy 

 borders approaching, but not passing beyond, G and H. With a 

 solution containing 1 part of blood in 100, the appearances differ 

 remarkably from those previously referred to. The solution is 

 transparent for light from F to nearly G ; it transmits light with 

 difficulty from L to N" (x 38l*9-X 35.0*01) ; the remainder of the ultra- 

 violet is completely absorbed. A solution containing 5 per cent, of 

 defibrinated blood (or about 6*5 parts of oxyhsemoglobin in 1000 parts) 

 absorbs the whole of the violet and ultra-violet regions of the spectrum, 

 with the exception of a region between F and G, but nearer the former 

 (X 460-X 490). 



It remains to be considered with how dilute a solution of oxy- 

 hsemoglobin a photographic record of Soret's band can be obtained. 

 Examining a stratum 10 mm. broad I have obtained definite results, 

 when the solution contained somewhat, but not much, less than 1 part 

 of oxyhsemoglobin in 10,000. 



No colouring matter yet investigated exhibits the intense absorption- 

 band between G and H which is characteristic of haemoglobin and its 

 compounds. Several substances (carmine, picro-carmine, and the colouring 

 matter of alkanet root) exhibit absorption-bands in the visible part of 

 the spectrum which bear a superficial resemblance to those of oxy- 

 hsemoglobin. The spectrum of none of these colouring matters exhibits, 

 however, any absorption in the extreme violet or the adjacent ultra- 

 violet. 



The researches which I have conducted have shown that the band of 

 Soret depends on the iron-containing group existing in the haemoglobin 

 molecule, yet not upon its iron. The variations in character and position 

 which this band exhibits in the various compounds and derivatives of 

 haemoglobin will be referred to under each. 



