XIV.

Vegetable substances alone will not sustain life for a great length of time in every climate, but there is a vast difference between the wants of man at the equator and his necessities at the pole.

Nature requires for the working of her plans materials of diverse natures: neither the oil, nor starch, nor sugar, will sustain life alone. Chemical analysis and physiological history point out to us how positive is the law which fixes the component parts of grains and plants, and how imperative the necessity of adjusting in alimentation these forms of nutritive matter, which spring up on every side in profusion, and offer endless variety to the wants of man.

There must be harmony of certain principles; there must be union of starch, of gluten, and fat, to complete the process of digestion and assimilation. To feed a patient upon arrow-root, tapioca, or sago, and the like, is to consign him to certain death. Instinct impels us sometimes to make use of articles which our habits have thrown aside.