IV 



THE BLOOD : FOKMED CONSTITUENTS 



107 



phosphate and potassium chloride ; in man, and a few other 

 animals only, there is also a small amount of sodium chloride. 



The water content of the erythrocytes is very low as compared 

 with other organs. In man it reaches only 5 7 '7 per cent, while 

 in the muscles and glands it amounts to 75 per cent (Hoppe- 

 Seyler). 



The dry substance of the erythrocytes consists principally of 

 haemoglobin (87-95 per cent), so that the stroma is a very small 

 amount (13*5 per cent). For the total quantity of the blood, 

 about 13*8 per cent haemoglobin lias been calculated for man, and 

 about 12'6 per cent for woman. 



Hoppe - Seyler was the first to investigate the chemical 

 properties of haemoglobin (1860-71 ) and to recognise that although 

 it is a colloid body, it is 

 capable of crystallising in 

 different forms in different 

 animals, all, however, belong- 

 ing to the rhombic system 

 (with the exception of 

 squirrel's blood, which crys- 

 tallises in hexagonal plates ; 

 Fig. 32). To obtain crystals 

 of pure haemoglobin, they 

 must first be dissolved in the 

 blood by freezing and gradual 

 melting ; the blood in a layer 

 2 mm. deep is then allowed 

 to evaporate slowly in a flat, 

 wide-bottomed capsule. 



The different forms of 

 oxyhaemoglobin crystals, the 

 different quantities of water of crystallisation which they contain, 

 their different solubilities and different resistance to decomposing 

 agents, in short the varying results of elementary analysis, all point 

 to the conclusion that oxyhaemoglobin is not identical in different 

 animals. It is a highly complex, iron-containing protein, the 

 formula of which was determined by Hiit'ner from analysis of 

 the haemoglobin of dogs' blood. Each molecule of haemoglobin 

 combines with a molecule of oxygen to form oxyhaemoglobin. 



Haemoglobin has a greater affinity for carbonic oxide than for 

 oxygen, and forms with it carboxy haemoglobin, which, unlike 

 oxyhaemoglobin, doas not reduce with deoxidising agents. While 

 carbonic oxide turns out oxygen, the latter has difficulty in 

 driving carbonic oxide out of its combination with haemoglobin. 

 To this fact is due (in part, if not wholly) the toxic action of 

 carbon monoxide. 



With a series of oxidising agents, particularly with nitrites, 



52. Haemoglobin crystals. (Funke.) , From 

 man ; b, guinea-pig ; c, squirrel. 



