BY DR. BURDON-S ANDERSON. 1P5 



spectroscope. The first is. that when solutions of haemoglobin, 

 or of blood, are deprived of oxygen, either by placing them m 

 vacua or by the addition of reducing agents, the more refran- 

 gible rays (blue and violet) are much less absorbed, and the 

 green more absorbed than they were before. The second fact 

 is, that in solutions so concentrated that most of the spectrum 

 is extinguished, the last color which is transmitted is orange- 

 red if the blood is arterial, red if it is venous. These two facts 

 may be shortly expressed by saying that the color of arterial- 

 ized blood consists of orange-red plus green, of venous blood- 

 red plus blue. 



These differences, however, are not the most remarkable 

 which are observed when oxydized and reduced solutions of 

 blood or its coloring matter are compared spectroscopically. 

 The most striking change produced by reduction relates to the 

 two bands of absorption in the yellow part of the spectrum 

 which have been already mentioned. This change is most 

 readily demonstrated by following the directions given by 

 Stokes in his original, paper. A solution of protosulphate of 

 iron, to which a sufficient quantity of tartaric acid has been 

 added to prevent its being precipitated by alkalies, is rendered 

 decidedly alkaline by the addition of ammonia, and is intro- 

 duced into the solution of blood. " The color is almost in- 

 stantly changed to a much more purple red, as seen in small 

 thicknesses, and a much darker red than before, as seen in 

 greater thickness. The change of color, which recalls the dif- 

 ference between arterial and venous blood, is striking enough, 

 but the change in the absorption spectrum is far more decisive. 

 The two highly characteristic dark bands seen before, are now 

 replaced by a single band, somewhat broader and less sharply 

 defined at its edges than either of the former, and occupying 

 nearly the position of the bright band separating the dark bands 

 of the original solution (see Fig. 195, 2). The fluid is more 

 transparent for the blue, and less so for the green than it was 

 before. If the thickness be increased till the whole of the spec- 

 trum more refrangible than the red be on the point of disap- 

 pearing, the last part to remain is green, a little beyond the 

 fixed line 6, in the case of the original solution ; and blue, some 

 way beyond F, in the case of the modified fluid. If the purple 

 solution be exposed to the air in a shallow vessel, it quickly 

 returns to its original condition, showing the same two char- 

 acteristic bands as before ; and this change takes place imme- 

 diately, provided, a small quantity only of the reducing agent 

 were employed, when the solution is shaken up with air. If 

 an additional quantity of the reagent be now added, the same 

 effect is produced as at first, and the solution may thus be 

 made to go through its changes any number of times." [Stokes, 

 On the Reduction and Oxj'dation of the Coloring Matter of 



