CHAPTER X. 



THE RED BLOOD CORPUSCLES AND 

 THE BLOOD PIGMENTS. 



A. The Laking of Blood. 



The red corpuscles consist of an envelope and meshwork 

 called the stroma, which encloses a solution of haemoglobin 

 and various salts. The stroma consists of a protein, 

 probably a histone, with which is associated a lipoid 

 material, related to cholesterin and lecithin. The envelope 

 behaves as a semi-permeable membrane to a great many 

 solutions, readily allowing water to pass into or from the 

 corpuscle, but preventing the passage of most salts and 

 other dissolved substances. Thus, if the corpuscles are 

 placed in a solution which has a higher osmotic pressure 

 than the fluid within the corpuscles, water passes out of the 

 corpuscle, which therefore shrinks. Such fluids are called 

 " hypertonic." If they be placed in fluids of a lower 

 osmotic pressure ("hypotonic"), water passes into the 

 corpuscle to equalise the pressures, but salts cannot pass 

 out. The corpuscles swell and the expansion may be 

 sufficient to lead to the disruption of the envelope, so that 

 the enclosed haemoglobin passes into the body of the 

 solution. This bursting of the corpuscles is known as 

 taking or haemolysis. A solution of the same osmotic 

 pressure as that of the fluid within the corpuscle is said 

 to be "isotonic" or "normal." For mammalian blood 

 0-9 per cent, sodium chloride is normal ; for frog's blood, 

 0-65 per cent. Other physical means of inducing hae- 

 molysis are by repeatedly freezing and thawing the blood, 

 or by warming to 60 C. 



The envelopes can also be ruptured by chemical means. 

 Certain substances, such as the bile salts, ether, chloroform, 



