the all-important role of proteins, in either
plant or animal tissue, is to furnish the colloidal protoplasmic material
in which the vital phenomena take place. Their occurrence in seeds, and
other storage organs, is, of course, in order to provide the
protoplasm-forming material for the young seedling plant.

They are, moreover, the source for the material which goes into some of the
secretion groups of organic compounds; as they are easily broken down by
various agents of decomposition into nitrogen-free alcohols, aldehydes, and
acids, which produce the essential oils, pigments, etc.

Much, if not all, of their physiological activity is due to their colloidal
nature, the importance and effects of which will be more apparent after the
chapters dealing with the colloidal condition of matter and with the
physical chemistry of protoplasm have been studied.

REFERENCES

ABDERHALDEN, E.--"Neuere Ergebnisse auf dem Gebiete der Speziellen
Eiweisschemie," 128 pages, Jena, 1909.

FISCHER, E.--"Untersuchungen ueber Aminosaeuren, Polypeptide, und Proteine,
1899-1906," 770 pages, Berlin, 1906.

MANN, G.--"Chemistry of the Proteids," 606 pages, London, 1906.

OSBORNE, T. B.--"The Vegetable Proteins," 138 pages, _Monographs_ on
Biochemistry, London, 1909.

PLIMMER, R. H. A.--"The Chemical Constitution of the Proteins, Part I,
Analysis," 188 pages; and "Part II, Synthesis, etc." 107 pages,
_Monographs_ on Biochemistry, London, 1917. (3d ed.).

ROBERTSON, T. B.--"The Physical Chemistry of the Proteins," 477 pages, New
York, 1918.

SCHRYBER, S. B.--"The General Characters of the Proteins," 86 pages,
_Monographs_ on Biochemistry, London, 1909.

UNDERHILL, F. P.--"The Physiology of the Amino-acids," 169 pages, 13 figs.
1 plate. Yale University Press, 1915.

CHAPTER XIV

ENZYMES AND THEIR ACTION

The characteristic difference between the reactions of inorganic compounds
and those of organic substances lies in the rapidity, or velocity, of the
chemical changes involved. Speaking generally chemical reactions take place
between substances which are in solution, so that they may come into
sufficiently intimate contact that chemical action between them can take
place. There are, of course, occasional examples of reactions between dry
solids, such as the explosion of gunpowder, etc., but the general rule is
that reacting materials