Vegetables differ from animal food -

(1) In containing a much greater proportion of material which for man is indigestible (cellulose), and a less proportion of nutritive material.

(2) The percentage of proteid is below that of animal food, and the proportion of carbohydrates is generally much greater, while the amount of fat is small, but varies considerably. In order, therefore, to get the required amount of nutritive material from a purely vegetable diet, it is necessary to consume a much greater quantity, and the amount of excrement indicating the indigestible matters is proportionately increased.