No mistake, said Huxley, is more frequently made by clever people than that of supposing that a cause or an opinion is unsound because the arguments put forward in its favour by its advocates are foolish or erroneous. Some of the arguments put forward in favour of the exclusive use by mankind of a vegetable diet can be shown to be based on misconception and error, and I propose now to mention one or two of these. But I wish to guard against the supposition that I am convinced in consequence that animal substances form the best possible diet for man, or that an exclusively vegetable diet may not, if properly selected, be advantageous for a large majority of mankind. That question, as well as the question of the advantage of a mixed diet of animal and vegetable substances, and the best proportion and quantity of the substances so mixed, must be settled, as also the question as to the harm or good in the habitual use of small quantities of alcohol, by definite careful experiment by competent physiologists, conducted on a scale large enough to give conclusive results. The cogency of the arguments in favour of vegetarianism which I am about to discuss is another matter. In the first place it is very generally asserted by those who advocate a purely vegetable diet that man's teeth are of the shape and pattern which we find in fruit-eating or in root-eating animals allied to him. This is true. The warm-blooded hairy quadrupeds which suckle their young and are called "mammals" (for which word perhaps "beasts" is the nearest Anglo-Saxon equivalent) show in different groups and orders a great variety in their teeth. The birds of to-day have no teeth, the reptiles, amphibians, and fishes have usually simple conical or peg-like teeth, which are used simply for holding and tearing. In some cases the pointed pin-like teeth are broadened out so as to be button-like, and act as crushing organs for breaking up shell-fish. The mammals alone have a great variety and elaboration of the teeth. [Illustration: Fig. 21.--Side view of the skull of a clouded tiger (_Felis nebulosa_) to show the teeth. _inc. s._ The three incisors. _can. s._ Upper canine, corner-tooth, or dog-tooth. _can. i._ Lower canine. _m. s._ The four upper molars or cheek-teeth (called "grinders" in herbivorous animals). _m. i._ The three lower molars or cheek-teeth.] [Illustration: 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.]