NITROGENOUS COMPOUNDS 73 



entirely satisfactory. The proteoses and peptones are, no 

 doubt, derived from other proteins, but they might well be 

 regarded as native, inasmuch as they occur in nature. The 

 polypeptides and amino-acids are also derived from proteins 

 by natural as well as by artificial processes, but they are not 

 generally regarded as members of the protein class. 



Albumins and Globulins. These occur together in most 

 of the tissues and fluids of both animals and plants. Albumins 

 appear to be converted into globulins on prolonged dialysis 

 of their solutions at temperatures between 75 and 85 C. 

 Certainly they are very much alike. They differ chiefly in 

 regard to solubility. 



The albumins are soluble in pure distilled water, and are 

 not floculated when the solutions are saturated with common 

 salt or magnesium sulphate. The globulins are insoluble in 

 pure water and in dilute acids ; but they are soluble in dilute 

 alkalis and in solutions of neutral salts. They are more easily 

 coagulated by heat than the albumins, and more readily 

 floculated by ammonium sulphate. They are completely 

 precipitated when their solutions are saturated with magnesium 

 sulphate and partially even by common salt. When pure, the 

 globulins have a faintly acid reaction. 



Particular specimens are generally named after the source 

 from which they are derived, e.g. serum albumin and serum 

 globulin from the serum of blood and lymph, lactalbumin and 

 lacto-globulin from milk, ovalbumin and ovoglobulin from 

 eggs, and so on. Fibrinogen and myosinogen and their 

 derivatives, fibrin and myosin, also most of the vegetable 

 proteins, e.g. edestin of hempseed, legumin of peas, and 

 conglutin of lupines, are all classed as globulins. Vegetable 

 albumins occur in cabbage and other plants. 



The fibrinogen of blood on exposure to air is rapidly 

 dissociated into fibrin and another protein called " fibrin 

 globulin." The former appears as a voluminous curdled mass, 

 while the latter remains in solution. The clotting of blood is 

 due to this change. It is caused by the action of a ferment 

 which is normally present in the blood. The change is not of 

 the nature of coagulation both of the products can be 



