198 PRACTICAL PHYSIOLOGY 



position they yield large amounts of the diamino acids, especially 

 arginine. 



Histones have been obtained from various sources, but globin 

 of blood is the most important of the group. They are strongly basic 

 substances and resemble in their properties in part native protein, 

 in .part protamine and in part proteose. Their behaviour to heat 

 depends on the presence or absence of salts ; no coagulation takes 

 place when salts are absent. 



Biuret, xanthoproteic and Millon's reactions are given, and a 

 large yield of diamino acids, especially histidine, on decomposi- 

 tion. 



The group of native proteins has been already studied in the 

 preceding experiments with the egg-white solution. The main 

 difference between the albumins and the globulins is that of 

 solubility. It has also been shown chemically that the products of 

 hydrolysis differ, the albumins yielding no glycin. Upon hydrolysis 

 all yield members of the chief amino acid groups. 



Albumins are soluble in distilled water and in saturated solutions 

 of all neutral salts except ammonium sulphate and anhydrous 

 sodium sulphate, in which they are insoluble. They are, however, 

 soluble in half -saturated solutions of these salts. 



Globulins are insoluble in distilled water and in saturated solutions 

 of all neutral salts. They are, moreover, insoluble in half -saturated 

 solutions of ammonium sulphate and anhydrous sodium sulphate. 

 They are soluble in weak saline solutions. 



The chief kinds of albumins are egg albumin, serum albumin (see 

 Blood), and lactalbumin (see Milk). 



The most important globulins are egg globulin, serum globulin, 

 fibrinogen (for both see Blood), and myosinogen (see Muscle). 



Plant Proteins. This comprises the two groups (a) Glutelins and 

 (6) Gliadins (Prolamines), and they form the bulk of the protein 

 present in such cereals as wheat, barley, maize, etc. The so-called 

 gluten of wheat is composed of approximately equal amounts of 

 the two groups. The glutelins are insoluble in water and in dilute 

 neutral salt solution, but are soluble in dilute acids and alkalis. 

 They are coagulable on heating. The gliadins are insoluble in 

 water and in absolute alcohol but dissolve in about 70 per cent, 

 alcohol. They are insoluble in dilute neutral salt solutions. They 

 have been called prolamines because they have been shown to be 

 rich in the amino acid proline (pyrrolidine carboxylic acid) and 

 amide groups. They are also rich in glutamic acid. 



Phosphoproteins. The chief members of this group are the 

 caseinogens of milk and the vitellins from egg-yolk. They derive 

 their name from the large amount of phosphorus contained in 

 their molecule. They differ, however, from nucleoproteins in con- 

 taining no purin bases. 



Dissolve some commercial caseinogen in 2 per cent, caustic soda, 

 and perform the following experiments : 



