CH. XXVI.] 



HAEMOGLOBIN 



429 



potassium and sodium, and phosphates of calcium and magnesium. 

 In man potassium chloride is more abundant than sodium chloride ; 

 this, however, does not hold good for all animals. 



Oxygen is contained in combination with the haemoglobin to form 

 oxyhsemoglobin. The corpuscles also contain a certain amount of 

 carbonic acid. 



Haemoglobin and Oxyhaemoglobin. The pigment is by far 

 the most abundant and important of the constituents of the red 

 corpuscles. It is a substance which gives the reactions of a proteid, 

 but differs from most other proteids in containing the element iron, 

 and in being readily crystallisable. 



It exists in the blood in two conditions : in arterial blood it is 

 combined loosely with oxygen, is of a bright red colour, and is called 

 oxyhsemoglobin; the other con- 

 dition is the deoxygenated or re- 

 duced 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 return- 

 ing to the heart after it has sup- 

 plied the tissues with oxygen. 

 Venous blood, however, always 

 contains a considerable quantity 

 of oxyhaemoglobin also. Haemo- 

 globin is the oxygen-carrier of 

 the body, and it may be called a 

 respiratory pigment.* 



Crystals of oxyhsemoglobin -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 follow- 

 ing 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 corpuscles 

 are rendered colourless, and then the oxyhsemoglobin crystallises out 

 from the solution so formed. 



2. Microscopical specimens may also be made by Stein's method, 



: 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. 362. Crystals of oxyhaemoglobin prismatic, 

 from human blood. 



