THE COMPONENTS OF PLANTS AND ANIMALS 33 



teins. The principal groups into which they are subdivided are 

 designated as follows : 



a. Albumins. These are simple proteins soluble in pure 

 water and coagulable by heat. Besides the familiar egg al- 

 bumin, they include the albumins of blood serum and of milk 

 serum. Albumins have also been found in small amounts in 

 a great variety of seeds, including those of wheat, rye, barley, 

 pea, vetch, soybean and cowpea. 



b. Globulins. The globulins are simple proteins insoluble 

 in pure water but soluble in neutral solutions of salts of strong 

 bases with strong acids. Globulins are found in the lymph 

 and the blood serum and in the muscles and other organs, but 

 they appear to be especially characteristic of the vegetable 

 kingdom, occurring in considerable amounts in a large number 

 of seeds. Osborne 1 gives a list of 1 5 globulins occurring in 24 

 different species of seeds and enumerates 12 additional species 

 which contain globulins to which no distinctive names have 

 yet been given. 



c. Glutelins. These are defined as simple proteins insoluble 

 in all neutral solvents but readily soluble in very dilute acids 

 and alkalies. The only well-defined members of this group at 

 present known are the glutenin of wheat and the oryzenin of 

 rice, although there seems reason to believe that similar pro- 

 teins exist in the seeds of other cereals. 



d. Prolamins, or alcohol-soluble proteins. The typical mem- 

 ber of this group is the gliadin of wheat and the name has 

 been applied by some authors to the entire group, but the 

 term prolamins, proposed by Osborne, seems preferable. The 

 prolamins are soluble in relatively strong alcohol (70-80 percent) 

 but insoluble in water, absolute alcohol and other neutral sol- 

 vents. They are characteristic of the seeds of the cereals, the 

 principal prolamins being the gliadin of wheat and rye, the 

 hordein of barley, the zein of maize and the bynin of malt. 



e. Albuminoids. This name, formerly used to a consider- 

 able extent as practically synonymous with proteins, is now 

 applied to two groups of nitrogenous substances which have 

 been otherwise designated as the collagens, or gelatinoids, and 

 the keratins. Albuminoids are defined as simple proteins which 

 possess essentially the same chemical structure as the other 



1 The Vegetable Proteins, p. 78. 



