454 HAEMOGLOBIN. [Book ii. 



also be removed from the haemoglobin not only by physical but 

 also by chemical means, as by the use of reducing agents. Thus 

 if a few drops of ammonium sulphide or of an alkaline solution 

 of ferrous sulphate, kept from precipitation by the presence of 

 tartaric acid, be added to a solution of haemoglobin, or even to 

 an unpurified solution of blood corpuscles such as is afforded 

 by the washings from a blood clot, the oxygen in loose combi- 

 nation with the haemoglobin is immediately seized upon by the 

 reducing agent. This may be recognized at once, by the char- 

 acteristic change of colour ; from a bright scarlet the solution 

 becomes of a purplish claret colour, when seen in any thickness, 

 but greenish when sufficiently thin : the colour of the reduced 

 solution is exactly like that of the crystals from which the 

 loose oxygen has been removed by the air-pump. 



Examined by the spectroscope, this reduced solution, or 

 solution of reduced hcemoglobin, as we may now call it, offers a 

 spectrum (Fig. 89, 5) very different from that of the unreduced 

 solution. 



The two absorption bands have disappeared, and in their 

 place there is seen a single, much broader, but at the same time 

 much fainter band, whose middle occupies a position about mid- 

 way between the two absorption bands of the unreduced solu- 

 tion, though the redward edge of the band shades away rather 

 farther towards the red than does the other edge towards the 

 blue ; its centre corresponds to about wave-length 555. At 

 the same time the general absorption of the spectrum is differ- 

 ent from that of the unreduced solution ; less of the blue end 

 is absorbed. Even when the solutions become tolerably con- 

 centrated, many of the bluish-green rays to the blue side of 

 the single band still pass through. Hence the difference in 

 colour between haemoglobin which retains the loosely combined 

 oxygen, 1 and haemoglobin which has lost its oxygen and become 

 reduced. In tolerably concentrated solutions, or tolerably thick 

 layers, the former lets through the red and the orange-yellow 

 rays, the latter the red and the bluish-green rays. Accordingly, 

 the one appears scarlet, the other purple. In dilute solutions, 

 or in a thin layer, the reduced haemoglobin lets through so 

 much of the green rays that they preponderate over the red, 

 and the resulting impression is one of green. In the unreduced 

 haemoglobin or oxyhemoglobin, the potent yellow which is 

 blocked out in the reduced haemoglobin, makes itself felt, so 

 that a very thin layer of oxyhemoglobin, as in a single cor- 

 puscle seen under the microscope, appears yellow rather than 

 red. 



It must be remembered that when we speak of reduced 



1 For brevity's sake we may call the haemoglobin containing oxygen in loose 

 combination, oxyhemoglobin, and the haemoglobin from which this loosely com- 

 bined oxygen has been removed, reduced haemoglobin or simply haemoglobin. 



