462 



THE BLOOD 



[CH. XXIX. 



oxyhaemoglobin ; the other condition is the deoxygenated or reduced 

 haemoglobin (better called simply haemoglobin). This is found in the 

 blood after asphyxia. It also occurs in all venous blood that is, 

 blood which is returning to the heart after it has supplied the 

 tissues with oxygen. Venous blood, however, always contains a con- 

 siderable quantity of oxyhaemoglobin also. Haemoglobin is the oxygen - 

 carrier of the body, and it may be called a respiratory pigment.* 



Crystals of oxyhaemoglobin f may be obtained with readiness 

 from the blood of such animals as the rat, guinea-pig, or dog ; with 

 difficulty from other animals, such as man, ape, and most of the 

 common mammals. The following methods are the best : 



1. Mix a drop of defibrinated blood of the rat on a slide with 

 a drop of water; put on a cover-glass; in a few minutes the cor- 

 puscles are rendered colourless, 

 and then the oxyhaemoglobin 

 crystallises out from the solution 

 so formed. 



2. Microscopical specimens 

 may also be made by Stein's 

 method, which consists in using 

 Canada balsam instead of water 

 in the foregoing experiment. 



3. On a larger scale, crystals 

 may be obtained by mixing the 

 blood with one-sixteenth of its 

 volume of ether; the corpuscles 

 dissolve, and the blood assumes a 

 laky appearance. After a period 

 varying from a few minutes to 

 days, abundant crystals are de- 

 posited. 



In nearly all animals the crystals are rhombic prisms (fig. 327) ; 

 but in the guinea-pig they are rhombic tetrahedra, or four-sided 

 pyramids (fig. 328); in the squirrel and hamster, hexagonal plates 



^ The crystals contain a varying amount of water of crystallisation ; 

 this probably explains their different crystalline form and solubilities. 

 Several observers have analysed haemoglobin. They find carbon, 

 hydrogen, nitrogen, oxygen, sulphur, and iron. The percentage of 



* In the blood of invertebrate animals haemoglobin is sometimes found, but 

 usually in the plasma, not in special corpuscles. Sometimes it is replaced by other 

 respiratory pigments, such as the green one, chlorocruorin, found in certain worms, 

 and the blue one, haemocyanin, found in many molluscs and Crustacea. Chloro- 

 cruorin contains iron ; haemocyanin contains copper. 



t Crystals of haemoglobin can also be obtained by carrying out the crystal- 

 lisation in an atmosphere free from oxygen. 



FIG. 327. Crystals of oxyhsemoglobin prismatic, 

 from human blood. 



