The human stomach is so constituted that it can digest but very little of raw food. Just as the nutritive part of the pea is enclosed by a _hull_, so in every organic food the nutritive element proper is contained in a hull, called _cell_. The nutritive element of the potato, for example--the starch--is enclosed in millions of small cells, which are indigestible for our stomach. By means of good magnifying glasses, these cells, invisible to the naked eye, may be plainly seen. If the potato were eaten raw, these cells, together with the nutritive element in them, would leave the body unchanged. But if the potato is boiled, fried, or baked, the cells, by their expansion from the heat, burst, and thus allow the starch to be free. Now, while animals have been given a digestive apparatus strong enough to dissolve the hardest cells--pigeons, for example, swallow and are able to digest raw pease--man has been endowed with intelligence which enables him to prepare his food artificially. Cooking, therefore, is as natural to man as the act of chewing; for chewing, the crushing of food with the teeth, on the part of animals that live on plants, is nothing but the tearing asunder of cells. Animals that have no teeth, birds for example, possess immensely strong powers of digestion. It would be as unnatural for the ox, who has good teeth to crush peas with, to swallow them entire as the pigeon does, as it were unnatural for man to take pease raw while he has the means of cooking them. We often call _art_ what really is _nature_ in man; for his mental gifts are natural to him; women, therefore, when they perform the art of cooking, practise a natural art. CHAPTER XII. NECESSITY FOR VARIETY IN FOOD. Let no one believe that it is from mere daintiness that man is fastidious in regard to food, and that he lives on a great variety of victuals. The human body is the transformed food which he has eaten. It is quite correct that man can live on bread and water a long time; but man's nature is so varied, his qualities are of such numerous kinds; his character, his impulses and passions, his wishes and desires, his thoughts and labors, are so infinitely varified and so much exposed to change, that man's body, the bearer of all these elements, must also be formed from material of the most diversified kind.