Fig. 22.—View in the horizontal plane of the teeth of the lower and upper jaw of the same clouded tiger's skull. inc. i. Lower incisors. inc. s. Upper incisors. can. i. and can. s. Lower and upper canine. m. The cheek-teeth—three only in the lower jaw, a minute fourth molar present in the upper.
In shape and size, as well as in number, the teeth of mammals are very clearly related to the nature of their food in the first place, and secondly to their use as weapons of attack or of defence. When the surface of the cheek-teeth is broad, with low and numerous tubercles, the food of the animal is of a rather soft substance, which yields to a grinding action. Such substances are fruits, nuts, roots, or leaves, which are "triturated" and mixed with the saliva during the process of mastication. Where the vegetable food is coarse grass or tree twigs, requiring long and thorough grinding, transverse ridges of enamel are present on the cheek-teeth, as in elephants, cattle, deer, and rabbits (see Figs. 8, 17, 19). Truly carnivorous animals, which eat the raw carcases of other animals, have a different shape of teeth. Not only do they have large and dagger-like canines or "dog-teeth" as weapons of attack, but the cheek-teeth (very few in number) present a long, sharp-edged ridge running parallel to the length of the jaw, the edges of which in corresponding upper and lower teeth fit and work together like the blades of a pair of scissors. The cats (including the lions, tigers and leopards) have this arrangement in perfection (see Figs. 21 and 22). They cut the bones and muscles of their prey into great lumps with the scissor-like cheek-teeth, and swallow great pieces whole without mastication. Insect-eating mammals have cheek-teeth with three or four sharp-pointed tubercles standing up on the surface. They break the hard-shelled insects and swallow them rapidly. The fish-eating whales have an immense number of peg-like pointed teeth only. These serve as do those of the seals—merely to catch and grip the fish, which are swallowed whole.
It is quite clear that man's cheek-teeth do not enable him to cut lumps of meat and bone from raw carcases and swallow them whole, nor to grip live fish and swallow them straight off (Pl. VI). They are broad, square-surfaced teeth, with four or fewer low rounded tubercles fitted to crush soft food, as are those of monkeys (see Pl. VII and its description). And there can be no doubt that man fed originally, like monkeys, on easily crushed fruits, nuts, and roots. He could not eat like a cat.
A fundamental mistake has arisen amongst some of the advocates of vegetarianism by the use of the words "carnivorous" and "flesh-eating" in an ill-defined way. Man has never eaten lumps of raw meat and bone, and no one proposes that he should do so to-day. Man did not take to meat-eating until he had acquired the use of fire, and had learnt to cook the meat before he ate it. He thus separated the bone and intractable sinew from the flesh, which he rendered friable and divisible by thorough grilling, roasting, or baking. To eat meat thus altered, both chemically and in texture, is a very different thing from eating the raw carcases of large animals. Man's teeth are thoroughly fitted for the trituration of cooked meat, which is, indeed, as well suited to their mechanical action as are fruits, nuts, and roots. Hence we see that the objection to a meat diet based on the structure of man's teeth does not apply to the use of cooked meat as diet. The use by man of uncooked meat is not proposed or defended.
Yet, further, it is well to take notice of the fact that there are many vegetarian wild animals which do not hesitate to eat certain soft animals or animal products when they get the chance. Thus, both monkeys and primitive men will eat grubs and small soft animals, and also the eggs of birds. Whilst the cat tribe, in regard to the chemical action of their digestive juices, are so specialised for eating raw meat that it is practically impossible for them to take vegetable matter as even a small portion of their diet, and whilst, on the other hand, the grass-eating cattle, sheep, goats, antelopes, deer and giraffes are similarly disqualified from any form of meat-diet, most other land-mammals can be induced, without harm to themselves, to take a mixed diet, even in those cases where they do not naturally seek it. Pigs, on the one hand, and bears, on the other, tend naturally to a mixed diet. Many birds, under conditions adverse to the finding of their usual food, will change from vegetable to animal diet, or vice-versâ. Sea-gulls normally are fish-eaters, but some will eat biscuit and grain when fish cannot be had. Pigeons have been fed successfully on a meat diet; so, too, some parrots, and also the familiar barn-door fowl. Many of our smaller birds eat both insects and grain, according to opportunity. Hence it appears impossible to base any argument against the use of cooked meat as part of man's diet upon the structure of his teeth, or upon any far-reaching law of Nature which decrees that every animal is absolutely either fitted (internally and chemically, as well as in the matter of teeth) for a diet consisting exclusively of vegetable substances, or else is immutably assigned to one consisting exclusively of animal substances. There is no à priori assumption possible against the use as food by man of nutritious matter derived from animals' bodies properly prepared.
So far as à priori argument has any value in such a matter, it suggests that the most perfect food for any animal—that which supplies exactly the constituents needed by the animal in exactly right quantity and smallest bulk—is the flesh and blood of another animal of its own species. This is a startling theoretical justification—from the purely dietetic point of view—of cannibalism. It is, however, of no conclusive value; the only method which can give us conclusions of any real value in this and similarly complex matters is prolonged, full, well-devised, well-recorded experiment. At the same time, we may just note that the favourite food of the scorpion is the juice of the body of another scorpion, and that the same preference for cannibalism exists in spiders, many insects, fishes, and even higher animals.
Another line of argument by which some advocates of vegetarianism appeal to the popular judgment is by representing flesh-food derived from animals as something dirty, foul, and revolting, full of microbic germs, whilst vegetable products are extolled as being clean and sweet—free from odour and putrescence and from the scaremonger's microbes. This, I perhaps need hardly say, is a gigantic illusion and misrepresentation. I came across it the other day in a very unreasonable pamphlet on food by the American writer, Mr. Upton Sinclair. Putrefactive microbes attack vegetable foods and produce revolting smells and poisons in them, just as they do in foods of animal origin. It is true that on the whole more varieties of vegetable food can be kept dry and ready for use by softening with hot water than is the case with foods prepared from animals. This is only a question of not keeping food too long or in conditions tending to the access of putrefactive bacteria. It is, on the whole, more usual and necessary, in order to render it palatable, to apply heat to flesh, fish, and fowl than to fruits. And it is by heat—heat of the temperature of boiling water—applied for ten minutes or more, that poison-producing and infective bacteria are killed and rendered harmless. More people have become infected by deadly parasites and have died from cholera and similar diseases, through having taken the germs of those diseases into their stomachs with raw and over-ripe fruit or uncooked vegetables and the manured products of the kitchen garden, than have suffered from the presence of disease-germs or putrefactive bacteria in well-cooked meat. Here, in fact, "cooking" makes all the difference, just as it does in the matter we were discussing above of the fitness of flesh and bone for trituration by man's teeth.