CHAP, ii.] RESPIRATION. 593 



Examined by the spectroscope, this reduced solution, or solution 

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

 (Fig. 75, 5) very different from that of the unreduced solution. 



The two absorption bands have disappeared, and in thenplace 

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

 fainter band, whose middle occupies a position about midway 

 between the two absorption bands of the unreduced solution, 

 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 different from that of 

 the unreduced solution; less of the blue end is absorbed. Even 

 when the solutions become tolerably concentrated, 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 oxyhaemoglobin, the 

 potent yellow which is blocked out in the reduced haemoglobin, 

 makes itself felt, so that a very thin layer of oxyhaemoglobin, as in 

 a single corpuscle seen under the microscope, appears yellow 

 rather than red. 



It must be remembered that when we speak of reduced 

 haemoglobin (or more briefly haemoglobin), with a purple colour 

 and a characteristic one-banded spectrum, we mean haemoglobin 

 which has lost all its loosely associated oxygen. If a quantity of 

 oxyhaemoglobin be exposed to an insufficiently low pressure, or to 

 the action of an insufficient quantity of the reducing action, it 

 gives up a part only of its oxygen ; it is only partly reduced. 

 Such a partly reduced solution still shews the two bands of 

 oxyhaemoglobin. 



347. When the haemoglobin solution (or crystal) which has 

 lost its oxygen by the action either of the air-pump or of a reducing 

 agent or by the passage of an indifferent gas, is exposed to air 

 containing oxygen, an absorption of oxygen at once takes place. 

 If sufficient oxygen be present, the haemoglobin seizes upon 

 sufficient oxygen to obtain its full complement, each gramme 

 taking up in combination T59 c.cm. of oxygen; if there be an 

 insufficient quantity of oxygen the haemoglobin still remains partly 



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

 combination, oxy haemoglobin, and the haemoglobin from which this loosely combined 

 oxygen has been removed, reduced haemoglobin or simply haemoglobin. 



