In his work on digestion he seems to regard man as naturally an omnivorous animal; and, taking this for granted, he speaks as follows respecting his diet:
"One would hardly assert that even in temperate climates his (man's) system requires animal food. I doubt whether any instance can be adduced—unless man be regarded as such—of an omnivorous animal incapable of being adequately nourished by a sufficient and proper vegetable diet.
"Man, dwelling in a temperate climate, and with the power to choose, almost uniformly employs a mixture of animal and vegetable food; but how much early education may have to do in forming his taste for a mixed diet it is difficult to estimate. Habit has certainly great influence in attaching us to particular kinds of aliment. One who has long been accustomed to animal food cannot at once abstain from it without experiencing some feebleness for the want of its stimulation, and perhaps even temporary emaciation. And, on the other hand, he who has long been confined to a vegetable diet is apt to lose his relish for flesh, and, on recurring suddenly to its use, to find it too exciting.
"The liberal use of animal food has been generally thought requisite in arctic climes, to stimulate the functions, and thus furnish a more abundant supply of animal heat, to preserve against the extremity of external temperature. Northern voyagers mostly believe that fat animal food and oils are essential to the maintenance of health and life in the inhabitants of those frozen regions. But to me it would seem that their habits, in respect to diet, prove the capabilities, rather than the necessities, of their systems. They learn to eat their coarse fare because they can get no other. Their food, moreover, as is generally the case in savage life, is precarious; and thus, being at times exposed to extreme want, they are stimulated to greater excesses when their supplies are ample.
"The fact of man's dwelling in them (the arctic regions), and eating what he can get there, no more proves him to be naturally a flesh-eating animal than the circumstance of some cattle learning to eat fish, when they are in situations where they can obtain no other food, proves them to be piscivorous.
"Haller conceived it necessary that human life should be sustained by animal and vegetable food, so apportioned that neither should be in excess; and he asserts that abstinence from animal food causes great weakness in the body, and usually a troublesome diarrhœa. But such an opinion is certainly incorrect, since not only particular individuals, but even numbers of people, dwelling in temperate climates, from various causes, subsist almost wholly on vegetable substances, and yet preserve their health and vigor.
"Were we educated to its exclusive use, I am persuaded that a vegetable diet would afford us ample support; but whether, if restrained from animal food, we should, as a consequence, in the course of time, and under equally favoring circumstances in other respects, rise still higher in our moral and physical nature, remains, as I conceive, to be proved."
These views of Dr. S. were repeated, in substance, in a course of lectures given by him at the Masonic Temple, in Boston, in 1838. It will be seen that he concedes what the friends of the vegetable system deem a very important point, viz., that man's whole powers, physical, intellectual, and moral, can be well developed on a diet exclusively vegetable. We do not ask him to grant more. If man is as well off on vegetable food as without it, we have moral reasons of so much weight to place against animal food, as, when duly considered, will be, by all candid persons, sufficient to lead to its rejection.
True, we do not believe, with Dr. S.—at least I do not—that "whether a diet purely vegetable, or one comprehending both animal and vegetable food, would be most conducive to health, longevity, and intellectual, moral, and physical development, is a question only to be determined by a long course of experiments, made by various individuals in equal health, and placed, in all other respects, under as nearly similar circumstances as practicable." I believe this course of experiment does not remain to be made, but that it has been made, most fully, during the last four or five thousand years, and that the question is settled in favor—wholly so—of vegetable food. Still I do not ask physicians and other medical men to grant more than Dr. S. has; it is quite as much as we ought to expect of them.