The subject of food is one upon which countless experiments have been made by myriads of men during thousands and perhaps millions of years. In all parts of the world, from prehistoric times until now, men have been constantly engaged in finding out what things were good for them to eat and what things they had better avoid. The tendency to make such experiments begins at a very early period in life, and the first thing that a baby does with anything new is to carry it to its mouth so as to find out whether it is eatable or not. Nor must we forget that man is the last link in a chain whose beginnings reach to the earliest geological epochs, and that previous to man's appearance on earth those lower animals, from which he is in all probability descended, were also making experiments upon the subject of food.

Some animals developed completely into carnivora living upon flesh alone, like the lion; while others, like the ox, became entirely herbivorous. Man, however, is not restricted in his diet to either flesh alone or vegetables alone, but can live, when compelled by circumstances, on either of these dietaries or on a mixture of both.

The Indians of the Pampas, for example, are said to live for many months together entirely upon flesh, while many Hindoos are entirely vegetarians. The great majority of men, however, have a mixed diet, a large amount of it being of vegetable origin, but mixed, as circumstances allow, with the flesh of animals killed in the chase, or domestic animals, of birds, fishes, reptiles, insects and molluscs.