chap. xxvi. i SPECTROSCOPE IN PHYSIOLOGY. 327 



H.EMOGLOBIN. In solutions of a strength sufficient 

 with oxylipernoglobin to absorb all but the red and 

 orange rays of the spectrum, reduced haemoglobin will 

 permit the passage of the red and of some rays from 

 the green side of the absorption band. This fact ex- 

 plains the difference of colour between oxygenated 

 blood and blood from which the oxygen has been 

 removed, the former being of a bright red, the latter 

 of a purple claret colour owing to the passage of the 

 greenish rays and the absorption of the orange. If 

 the vessel retaining the reduced blood under examina- 

 tion be shaken with air for an instant, and immediately 

 re-examined, the double band will be seen, due to the 

 haemoglobin seizing on oxygen from the air. In a 

 short time, if the reducing agent be still acting on the 

 solution, the double band will give place to the single 

 band of reduced haemoglobin. This manoeuvre may 

 often be repeated with a like result. It is not to be 

 supposed that it is only arterial blood that gives the 

 band of oxyhaemoglobin. ; the double band is found 

 also in venous blood ; because all the oxviren. is not 



/ o 



removed in venous blood, much reduced hemoglobin 

 exists, but sufficient oxyhaemoglobin also to give the 

 two lines, which are more conspicuous than the single 

 band of reduced haemoglobin. 



If carbonic acid be substituted in the blood solu- 

 tion for oxygen, the spectrum still gives two bands 

 similar to those of oxy haemoglobin, but not occupying 

 precisely similar positions, though this is not ascer- 

 tained without careful measurement. The BANDS OF 

 CARBONIC OXIDE HAEMOGLOBIN are slightly displaced 

 towards the violet end of the spectrum ; and they do 

 not disappear on the addition of reducing agents. 



Haemoglobin when acted on by acids or alkalies 

 yields two substances, a proteid called globulin, and a 

 colouring matter, haematin. The haematin may be in 

 one of two conditions, according as acid or alkali has 



