240 THE RED BLOOD CORPUSCLES. [CTI. X. 



mix by inverting and allow the tubes to stand for a few minutes. 

 A will be translucent, the corpuscles being fully laked. F will be 

 opaque. Note the dilution which just causes laking. It is generally 

 about 0-55 per cent. 



NOTE. The solution that just causes laking is hypotonic to the blood, 

 indicating that the corpuscles can absorb a considerable quantity of fluid before 

 the envelope is ruptured. 



284. To 5 cc. of 0-9 per cent, sodium chloride add some ether 

 and shake vigorously. Then add three drops of blood, mix by 

 inversion. Warm gently and add a few more drops of ether. 

 The blood is laked. 



NOTE. It is essential that pure ether be used. Should the ether be 

 contaminated with acid the blood is precipitated and the pigment converted 

 to acid haematin. 



285. To a 0-2 per cent, solution of bile salts in normal saline 

 add three drops of blood. Mix and warm to 37 C. The blood is 

 generally laked, though the experiment does not always succeed. 



286. Add some blood to a 2 per cent, solution of urea in 

 water. The blood is laked. 



287. Repeat the experiment with a 2 per cent, solution of 

 urea in normal saline. The blood is not laked. 



NOTE. A solution of urea behaves like water as regards the corpuscles. 

 No matter what concentration is used the corpuscles take up water from the 

 surrounding fluid. In other words, the envelope of the corpuscle does not act 

 as a semipermeable membrane as regards urea. 



B. Haemoglobin and its Derivatives. 



Haemoglobin (Hb) is a compound protein, being a 

 member of the group of chromoproteins. It is formed by 

 the union of a pigmented non-protein substance containing 

 iron, and called haematin (Hn), with globin, a member 

 of the histone group of proteins. 



It is soluble in water and dilute salt solutions : in- 

 soluble in ether and alcohol. 



It is decomposed b}^ acids and alkalies into haematin 

 and globin. It is decomposed and coagulated by heat. 



