The importance of the invention of cookery relates almost entirely to its effect on vegetable food. It is probable that before man learnt the art he had already begun to prepare his vegetable food in other ways, as by sun-drying, grinding, and burying-processes which in many cases increase its digestibility, and by maceration, whereby poisonous and acrid ingredients may be got rid of. When he learnt to subject it to these various methods of preparation, but still more when he began systematically to apply artificial heat to it, i.e. to cook it, he greatly augmented his supply, for there are many highly nutritious vegetable substances which in the unprepared state, either on account of the large proportion of dense cellulose they contain or of their admixture with noxious substances, are of little or no food-value to him, but which by cooking and other means can be converted into valuable nutriment. Hence with advances in the art of cookery - and it is surprising to what a degree of excellence that art had attained in the latter part of this period - the supply of vegetable food steadily increased, and the hunter found himself to some extent released from the chase and freer to devote himself to other pursuits. These changes continued throughout the periods under consideration, until vegetable food came to constitute one-half, or more, of the total dietary.

1 The term "cibiculture" is convenient as signifying the cultivation of food, animal as well as vegetable.

The chief effect of cooking on vegetable food is to cause the starch granules to swell up and rupture the non-digestible cellulose chambers in which they, as well as the protein and fats, are contained. It is for this reason, and also because starch is more digestible cooked than raw, that cooking greatly adds to the digestibility of all vegetable substances containing an abundance of cellulose, while at the same time it relieves the organs of mastication of much of their work. The systematic adoption of cookery, therefore, led man to subject his vegetable food to less mastication than before, with the result that its starchy ingredients underwent so much the less oral digestion, and inasmuch as with the advent of this period more starch was consumed than previously, it is clear that more undigested starch entered the stomach than had hitherto been the case.

The abandoning of, and the corresponding loss of power to digest in the raw state, the less digestible and less palatable kinds of vegetable foods which characterized the homo-simian and early hunting periods, went on with accelerated rate after man had once begun to subject his food to artificial preparation. Thus he came to depend less and less upon raw vegetable produce and finally to limit himself to the easily digested kinds only.