CHEMICAL COMPOSITION OF THE HUMAN BODY 33 



N 16.38$; O 20.93^; S 0.568^; Fe 0.336^. If haemo- 

 globin contained one atom of iron, the empirical formula 

 would be C 636 H 1025 N 164 181 S 3 Fe. 



Haemoglobin is soluble in water and crystallizes directly 

 from its aqueous solutions in red, double-refractive prisms 

 and needles. Haemoglobin solutions absorb the yellowish- 

 green light of the solar spectrum. This is characteristic of 

 haemoglobin and may serve for the detection of blood pig- 

 ment. 



Haemoglobin is decomposed and coagulated by heating. 

 It gives most of the proteid reactions. By boiling with 

 alkalies and lead acetate, however, it does not yield lead 

 sulphide. 



Haemoglobin forms more or less unstable compounds with 

 oxygen, carbonic oxide, and nitric oxide. The compound 

 with oxygen is called oxyhaemoglobin and is of great physio- 

 logical importance. 



Oxyhamoglobin contains one molecule of haemoglobin and 

 one of oxygen or two atoms of oxygen to each atom of iron. 

 The oxygen is held but feebly, for even at body temperature 

 the oxyhaemoglobin decomposes into haemoglobin (also 

 called reduced haemoglobin) and free oxygen. Oxyhaemo- 

 globin is also reduced by putrefying substances and by 

 ammonium sulphide. 



Oxyhaemoglobin has two absorption bands in the yellow- 

 green of the spectrum between the D and E lines. Reduced 

 haemoglobin has but one broad band in the yellow-green. 



Methcemoglobm is a stronger union of haemoglobin with oxygen. 

 It is formed by the addition of potassium ferricyanide to oxyhaemo- 

 globin; it is reduced by ammonium sulphide. It has four 

 absorption bands, one of which, situated in the red, is very 

 characteristic. 



The compounds of haemoglobin with carbon monoxide and 

 nitric oxide are of interest only as they are frequently the cause 

 of death. This is especially true of CO-hcemoglobin. Carbonic 

 oxide forms a stronger union with jjj^^globin than oxygen does ; 

 it therefore drives out from the ox^P^rffigfc^nthe oxygen which 

 is absolutely necessary for life. A solution oTCO-haemoglobin 

 has a cherry-red color and a spectrum similar to that of oxyhaemo- 



