50 A MANUAL OF PHYSIOLOGY 



quantity of oxygen is required to saturate both pigments, and this 

 evidence appears to be sound. The difference seems to lie rather in 

 the manner in which the oxygen is united to the haemoglobin 

 in the methaemoglobin molecule than in the quantity of oxygen 

 which it contains. For methaemoglobin, unlike oxyhaemoglobin, parts 

 with no oxygen to the vacuum, while, on the oiher hand, in the 

 presence of reducing agents it yields up its oxygen even more readily 

 than oxyhaemoglobin does (Haldane). 



By the action of acids or alkalies oxyhaemoglobin is split into 

 haematin and proteid bodies, of which the exact nature is little known. 

 When the haemoglobin is acted on by acids in the absence of oxygen, 

 haemochromogen is first formed, which then gradually loses its iron 

 and is changed into haematoporphyrin. If oxygen be present, 

 haematin is the final product By the action of alkalies reduced 



FIG. 10. DIAGRAM TO SHOW THE CHIEF CHARACTERISTICS BY WHICH 

 HAEMOGLOBIN AND SOME OF iTS DERIVATIVES MAY BE RECOGNISED 

 SPECTROSCOPICALLY. THE POSITION OF THE MIDDLE OF EACH BANI> 

 IS INDICATED ROUGHLY BY A VERTICAL LlNE. 



haemoglobin yields hamochromogen, which is stable in alkaline solu- 

 tion, and gives a beautiful spectrum with two bands, bearing some 

 resemblance to those of oxyhaemoglobin, but placed nearer the violet 

 end. The band next the red end of the spectrum is much sharper 

 than the other. 



Hamatin, the most frequent result of the splitting up of haemo- 

 globin, is generally obtained as an amorphous substance with a bluish- 

 black colour and a metallic lustre, insoluble in water, but soluble in 

 dilute alkalies and acids, or in alcohol containing them. In addition 

 to the iron of the haemoglobin, haematin contains the four chief 

 elements of proteid bodies, carbon, hydrogen, nitrogen and oxygen. 



Hczmatoporphyrin, or iron-free haematin, may be obtained from 

 blood or haemoglobin by the action of strong sulphuric acid. Its 

 spectrum in acid solution shows two bands, one just to the left of D, 

 the other about midway between D and E. Like oxyhaemoglobin, re- 

 duced haemoglobin, carbonic oxide haemoglobin, methaemoglobin and 

 other derivatives of haemoglobin, it also has a band in the ultra-violet. 



Hamin is a compound of haematin and hydrochloric acid, which 



