PROTEINS 111 



Albumins. The albumins are found widely distributed in 

 nature. Serum albumin in the blood, ovalbumin in egg-white, 

 lactalbumin in milk and myogen in muscle are the best known 

 members of this group. Compounds resembling the albumins 

 have been found in plants, although they differ in some of their 

 properties from the animal albumins. Albumins contain no 

 glycocoll, and relatively much sulphur (about 1.6-2.2%). They 

 are soluble in water and dilute salt solutions, are precipitated by 

 strong mineral acids, by saturation with ammonium sulphate in 

 neutral solution and by many other precipitants. They are 

 not precipitated by saturating a neutral solution with mag- 

 nesium sulphate or sodium chloride, but if such a solution is 

 acidified, the albumins precipitate. Albumins in solution coagu- 

 late on boiling, if salts are present and if the solution is faintly 

 acid. 



Globulins. Globulins also are widely distributed in nature, 

 both in animals and in plants. They often are associated with 

 albumins. Important members of the group are serum globu- 

 lin, fibrinogen and its derivative fibrin of the blood, and myosin 

 of the muscles, ovoglobulin in eggs, lactoglobuliii in milk, neuro- 

 globulin in nerve tissue, and several plant globulins such as 

 edestin from hemp seed, legumin from peas, lentils, etc., and 

 various others from nuts or other materials. 



The globulins are insoluble in pure water, and they may be 

 precipitated by pouring a solution of a globulin into a large 

 volume of pure water, or by dialyzing out the salts against dis- 

 tilled water through a parchment membrane. Globulins also 

 differ from albumins in containing glycocoll, and in the greater 

 ease with which they precipitate on the addition of a neutral 

 salt. Thus they are precipitated by half saturation with am- 

 monium sulphate or by saturation with magnesium sulphate or 

 sodium chloride in neutral solution. 



Fibrinogen has the property of clotting or coagulating, and is 

 responsible for the clotting of the blood. If freshly drawn blood 

 is stirred or beaten, the fibrinogen collects in stringy masses 

 called fibrin. If washed free from corpuscles fibrin is a white, 



