THE CORPUSCLES OF THE BLOOD 91 







evaporation the chloroform or ether extract deposits crystals of 

 oxyhaemoglobin . 



Crystals are readily obtained from the blood of the squirrel, rabbit, 

 and also from the mouse and rodents generally ; less readily from 

 man, horse, cat, birds, and fishes. It is a more difficult matter to 

 obtain crystals from the blood of the sheep, ox, and pig. 



The crystals vary in size and shape according to the animal from 

 which they are prepared (Fig. 21). Those from the rat are needle- 

 shaped, resembling those from human blood; from the guinea-pig 

 they are quadrilateral prisms; from the squirrel, hexagonal plates. 



The rosy colour and plump look of health is due to a plentiful 

 supply of well-oxygenated blood in the face. The great function of 

 the red corpuscle is to carry oxygen, and the most characteristic 

 property of the pigment haemoglobin is its power to form a loose 

 chemical combination with oxygen. The body thus formed is termed 



FIG. 21. CRYSTALS o? OXYH^IIOGLOBIN FROM HORSE'S BLOOD. 



oxyhsemoglobin, and it is to this body that the bright red colour of 

 arterial blood is due. If arterial blood, diluted, let us say, with water 

 to 1 in 500, is examined with the spectroscope, two absorption bands 

 are seen in the yellow and the green between the lines D and E (Fig. 22). 

 The addition of a reducing substance, such as ammonium sulphide, to 

 this solution displaces the oxygen from the oxyhaemoglobin. The 

 solution, now changed to a purplish colour, gives the spectrum of 

 haemoglobin; one broad but less dark band is seen between D and E 

 (Fig. 22). 



Carboxyhaemoglobin. Blood exposed to coal-gas or carbon mon- 

 oxide gives a spectrum resembling OHb, but the solution of COHb 

 is markedly pinker in colour, and is not reduced by the addition of 

 ammonium sulphide. This serves to distinguish the two. When a 

 solution of carboxyhaemoglobin is greatly diluted, it remains pink, 

 while that of oxyhaemoglobin diluted to the same extent becomes 

 yellowish-green . 



