so 



88 ESSENTIALS OF CHEMICAL PHYSIOLOaY 



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 3 2^00 ^^ch 

 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 



8^ ^ #% r^ shrink : they become crenated or wrinkled. 

 ^ ^ ^W^ vy The action of water and salt solution 

 suggests the existence of a membrane on 

 the surface of the corpuscles through which 

 osmosis takes place, but the existence of 



i IG. 29. — a-e, successive effects of . . 



water on a red blood corpuscle ; such a membrane is stiU a matter of dis- 



/, a red corpuscle crenated by salt . . , , 



solution; ^.action of tannin on cussion. if there IS no actual membrane, 

 the outer denser portion of the stroma plays 

 the role of one during osmotic phenomena. Dilute alkalis (0"2 per 

 cent, potash) dissolve the corpuscles. Dilute acids (1 per cent, 

 acetic acid) act like water, and in nucleated corpuscles 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 hsematin. 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 .... 



Solids I !^"g^^^^ • 

 ■ I morganic . 



100 parts of dried corpuscles contain — 



Proteid .... 



Haemoglobin 



Lecithin .... 



Cholesterin .... 



The proteid present appears to be identical with the nucleo- 

 proteid 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. 



