338 HMMOGLOBIN. [BOOK n. 



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 haemo- 

 globin 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. 



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 whole of the haemoglobin seizes upon its 

 complement, each gramme taking up in combination T59 c.cm. of 

 oxygen ; if there be an insufficient quantity of oxygen, a part only 

 of the haemoglobin gets its allowance and the remainder continues 

 reduced. If the amount of oxygen be sufficient, the solution (or 

 crystal), as it takes up the oxygen, regains its bright scarlet colour, 

 and its characteristic absorption spectrum, the single band being 

 replaced by the two. Thus if a solution of oxyhaemoglobin in a 

 test-tube after being reduced by the ferrous salt, and shewing the 

 purple colour and the single band, be shaken up with air, the 

 bright scarlet colour at once returns, and when the fluid is placed 

 before the spectroscope, it is seen that the single faint broad band 

 of the reduced haemoglobin has wholly disappeared, and that in its 

 place are the two sharp thinner bands of the oxyhaemoglobin. If 

 left to stand in the test-tube the quantity of reducing agent still 

 present is generally sufficient again to rob the haemoglobin of the 

 oxygen thus newly acquired, and soon the scarlet hue fades back 

 again into the purple, the two bands giving place to the one. 

 Another shake and exposure to air will however again bring back 

 the scarlet hue and the two bands ; and once more these may dis- 

 appear. In fact, a few drops of the reducing fluid will allow this 

 game of taking oxygen from the air and giving it up to the reducer 

 to be played over and over again, and at each turn of the game the 

 colour shifts from scarlet to purple, and from purple to scarlet, 

 while the two bands exchange for the one, and the one for the two. 



Colour of venous and arterial Blood. Evidently we have in 

 these properties of haemoglobin an explanation of at least one-half 



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

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

 oxygen has been removed, reduced haemoglobin or simply haemoglobin. 



