eins, in general, usually contain larger proportions of proline
and of glutamic acid than are found in animal proteins; also more arginine
than is found in any of the animal proteins except the protamines, which
contain as high as 85 per cent of this amino-acid.

Of the twenty-five plant proteins which have thus far been hydrolyzed and
studied from this standpoint, all contained leucine, proline,
phenylalanine, aspartic acid, glutamic acid, tyrosine, histidine, and
arginine; two gave no glycine; two others, no alanine; four contained no
lysine; and one, no tryptophane. Zein, the principal protein of corn
contains no glycine, lysine, or tryptophane. It is not sufficient to
support animal life and promote growth, if used as an exclusive source for
protein for food.

THE EXTRACTION OF PROTEINS FROM PLANT TISSUES

Since proteins are indiffusible, it is essential that the cell-walls of the
tissue shall be thoroughly ruptured as the first step in any process for
the extraction of these compounds from plant tissues. This is usually
accomplished by grinding the material as finely as possible, preferably
with the addition of sharp quartz sand, or broken glass, to aid in the
tearing of the cell-wall material.

The solvent to be used in extracting the proteins from this finely ground
material depends upon the nature and solubility of the proteins which are
present, and also upon whether it is desired to separate the proteins which
may be present in the plant, during the process of the extraction. A glance
at the scheme of classification of the proteins will show the following
solubilities which serve as a guide to the procedure to be followed: (_a_)
proteoses, albumins, and some globulins may be extracted with water; (_b_)
globulins and most of the water-soluble proteins may be extracted by using
a 10 per cent solution of common salt; (_c_) prolamines are extracted by
70-90 per cent alcohol; glutelins and prolamins dissolve in dilute acids or
dilute alkali.

A common procedure is to extract groups (_a_) and (_b_), using a 10 per
cent salt solution as the solvent, and then to separate the albumins,
globulins, etc., from this solution by suitable precipitants; then to treat
the material with 80 per cent alcohol, to extract the prolamines; and
finally with dilute alkali, to extract the glutelins. The dissolved
proteins in each extract can be subsequently purified by dialysis,
precipitation, etc. The insoluble pro