THE CORPUSCLES OF THE BLOOD 



87 



35 to 40 per cent, of the weight of the blood. This can be ascer- 

 tained by centrif uging blood in a fine graduated capillary tube known 

 as a hsematocrit. If done with a very rapid centrifuge, fresh blood 

 may be used ; otherwise oxalated or citrated blood is employed. 

 The number of corpuscles is greatly reduced in anaemia. Normally 

 there are 5,000,000 to 5,500,000 per cubic millimetre in man's blood, 

 4,500,000 to 5,000,000 in woman's blood (15 to 25 billions in the 

 whole blood of a man with a surface of 1,000 to 1,700 square metres). 

 The number per c.mm. varies from time to time; it is stated to be 

 diminished after drinking much fluid and during pregnancy, increased 

 after profuse sweating, after exercise, after hot and cold baths, in 

 the blood of the new-born, and in venous stasis. 



At high altitudes the number of the corpuscles and the Hb content 

 of the body is increased (see Fig. 18). 



Fia. 19. THE THOMA-ZEISS H^EMACYTOMETER. 



The red corpuscles undergo various changes in shape when sub- 

 mitted to the action of different substances. Distilled water causes 

 them to swell and bvirst (cf. Haemolysis); strong salt solution (hyper- 

 tonic) causes them to shrink and crinkle, or crenate ; tannic acid causes 

 the haemoglobin to leave the envelope and appear as a dot outside. 

 When blood is shed, the red corpuscles show a tendency to run together 

 into rolls like piles of coins. 



Enumeration of Red Corpuscles. This is done by an apparatus 

 known as a haemacytometer. The form generally employed is that 

 shown in Fig. 19. The apparatus consists of (1) two graduated mixing 

 pipettes, labelled 101 and 11 respectively; (2) a specially constructed 

 counting chamber. A small disc of glass (B) and a thicker plate of 

 glass (D) are affixed to a glass slide so as to form a platform (B) sur- 

 rounded by a well. When a cover-glass is placed over this plat- 

 form, a fine film-like space of known thickness is left between the 

 platform and the cover-glass. The platform is ruled in squares, 

 each T ^ of a square millimetre (C in Fig.). 



For counting red corpuscles the pipette labelled 101 is employed. 

 Blood is sucked up to the mark 1, and then quickly diluting fluid up 



