210 VETERINARY PHYSIOLOGY 



By placing the erythrocytes in a fluid of lower osmotic 

 equivalent, i.e. of lower molecular concentration, than the 

 blood plasma and corpuscles. A solution of 0*9 per cent, of 

 sodium chloride has the same osmotic equivalent as the plasma 

 and preserves the corpuscles unaltered ; in more dilute fluid 

 the corpuscles tend to swell up by endosmosis and the pigment 

 is dissolved out. Erythrocytes may therefore be used as a means 

 of determining the osmotic equivalent the molecular con- 

 centration of a fluid. 2nd. By the action of substances which 

 dissolve some constituent of the stroma, e.g. salts of the bile 

 acids (see p. 376), chloroform, ether, etc. 3rd. By Hsemolysins. 

 The serum of one animal contains a substance, destroyed by 

 heating to 55 C., which is haemolytic to the blood of animals 

 of other species, e.g. the serum of eels' blood contains a powerful 

 hsemolysin for rabbits' erythrocytes, and the serum of the dog a 

 less powerful one. Further, by injecting the blood or the 

 erythrocytes of one species of animal into another species, a 

 hsernolysin is developed which has a specific action on the 

 erythrocytes of the first species. 



Chemistry. The stroma of the erythrocytes is made up of 

 a globulin-like substance, in connection with which lecithin 

 and cholesterin occur in considerable quantities. Potassium 

 is the base most abundantly present. 



The pigment is Haemoglobin. It constitutes no less than 

 90 per cent, of the solids of the corpuscles. In many animals, 

 when dissolved from the corpuscles, it crystallises very readily. 

 The crystals prepared from the human blood are rhombic 

 plates. When exposed to air they are of a bright red colour, 

 but if placed in the receiver of an air-pump at the ordinary 

 temperature they become of a purplish tint. The same thing 

 occurs if the haemoglobin is in solution, or if it is still in the 

 corpuscles. The addition of any reducing agent such as 

 ammonium sulphide or a ferrous salt also causes a similar 

 change. This is due to the fact that hcemoglobin has an 

 affinity for oxygen, which it takes up from the air, forming a 

 definite compound of a bright red colour in which one mole- 

 cule of haemoglobin links with a molecule of oxygen, Hb0 2 , 

 and is known as oxyhaemoglobin. 



Haemoglobin is closely allied to the proteins, but differs 

 from them in containing 0'42 per cent, of iron. 



