Perhaps the most important factor of all, in considering this question of man’s natural diet, is the anatomical argument—the argument, that is, which says that man must or should naturally eat certain foods, for the reason that he belongs to the class or _genus_ of animals which lives upon that class of foods—and that, consequently, he should live upon them also. Comparative anatomy affords us one of the most tangible and at the same time one of the most forceful and convincing arguments that can be furnished in favour of man’s natural diet (whatever that may prove to be)—for the reason that its _facts_ are so well-attested that they cannot be gainsaid by anyone who is in possession of them; and only the _inferences drawn from these facts_ can be disputed—which is a question that will be considered later. As before stated, this line of argument is in many ways the most important with which we shall have to deal; it will tend either to condemn or to confirm my argument most strongly. From a scientific standpoint, the study of this subject is founded upon the fact that the diet of any animal, in its natural state, is always found to agree both with its anatomical structure and with its several digestive processes and general bodily functions. So clearly is this fact recognised, indeed, by comparative anatomists and scientists generally, that animals have been divided, according to their dietetic habits, into four great classes—herbivorous, frugivorous, carnivorous and omnivorous. There are various sub-and minor-divisions that can be and in fact are made—such as the gramnivora, or grain-eaters; the rodentia, or gnawers; the ruminants, or cud-chewers; and the edentata or creatures without teeth. These subdivisions need not concern us here, however; and I shall not discuss their anatomical structure or food-habits at any length. Their names sufficiently classify them—in a work of this nature, which deals with _foods_, and is not a natural history. For practical purposes, the gramnivora may be included in the class of frugivora—since most frugivorous animals eat grains to some extent. This understood, we can proceed to a consideration of the facts; and we shall see to which of these classes man belongs.