THE BLOOD 111 



They vary in size and structure in different groups of vertebrates. 

 In mammals they are biconcave (except in the camel tribe, where 

 they are biconvex) non-nucleated discs, in man averaging -g-^Ly- inch 

 in diameter ; during foetal life nucleated red corpuscles are, however, 

 found. In birds, reptiles, amphibians, and fishes they are biconvex 

 oval discs with a nucleus : they are largest in the amphibia. 



Water causes the corpuscles to swell up, and dissolves out the 

 red pigment (oxyhsemoglobin), leaving a globular colourless stroma. 

 Salt solution causes the corpuscles to , 



shrink : they become crenated or wrinkled. 

 The action of water and salt solution is 

 explained by the existence of a membrane 

 on the surface of the corpuscles through 

 which osmosis takes place. Dilute alkalis 



f FIG. 29. a-e, successive effects of 



(0'2 per Cent, potash) dlSSOive the COr- water on a red blood corpuscle : 



., 7 /- j.- /, a red corpuscle crenated by salt 



pUSCleS. JJliUte aCldS (1 per Cent, acetic solution ; g, action of tannin on 



acid) act like water, and in nucleated cor- 

 puscles render the nucleus distinct. Tannic acid causes a discharge 

 of haemoglobin from the stroma, but this is immediately altered and 

 precipitated. It remains adherent to the stroma as a brown globule, 

 consisting probably of haematin. Boric acid acts similarly, but in 

 nucleated red corpuscles the pigment collects chiefly round the 

 nucleus, which may then be extruded from the corpuscles. 

 Composition. 1,000 parts of red corpuscles contain 



Water . ... 688 parts 



Solids ! or g anic . ' 303 ' 88 



(inorganic . . . 8'12 ,, 



100 parts of dried corpuscles contain 



Protein . . . . . . 5 to 12 parts 



Haemoglobin . . . . 86 ,, 94 ,, 



Lecithin ..... 1*8 part 



Cholesterin . . . . . O'l 



The protein present appears to be identical with the nucleo- 

 protein of white corpuscles. The mineral matter consists chiefly of 

 chlorides of 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 

 oxyhaemoglobin. The corpuscles also contain a certain amount of 

 carbonic acid (see EESPIEATION, at the end of this lesson). 



The pigment of the red corpuscles, The pigment is by far the 



