Turning now to animal food it has to be remarked that while in the raw state it may be readily digestible with little or no previous mastication, since massive pieces of it are readily attacked by the digestive juices, the like is much less true of animal food the proteids of which have been coagulated and rendered less permeable by cooking. Large lumps of hard-boiled egg or overdone meat, for instance, may obstinately resist gastric digestion; indeed, as with vegetable so with animal foods, their relative digestibility depends more upon physical consistence than chemical composition; beef is generally more indigestible than mutton and pork or veal than either, not so much by virtue of chemical composition as of physical consistence; the indigestibility of cheese illustrates the same truth; the individual nutritive ingredients of this substance--the proteids and fats--are not in themselves indigestible; casein in the form of protein or plasmon is known to be easy of digestion, and butter is one of the most digestible of fats; but in cheese the two are welded together into a comparatively impermeable mass, which is apt to escape comminution by the teeth and to pass down into the stomach in the form of solid lumps. A plain, wholesome cheese well masticated or intimately mixed with other foods, as in macaroni cheese, is quite easily digested by the majority. I do not, of course, deny the influence of the chemical factor. Undoubtedly food may disturb digestion by virtue of its chemical composition, apart altogether from its physical characters; thus, while cooked goose-fat sets up violent irritation in some, others cannot tolerate eggs in any shape or form, and innumerable idiosyncrasies in respect of special articles of diet are met with which are essentially referable to chemical composition; but making due allowance for this chemical influence there can, I think, be little doubt that the digestibility of the more common articles of diet, both animal and vegetable, depends in the main upon their physical constitution, _all of them tending to be equally digestible when reduced to the same degree of comminution_. This, if true, is, I need scarcely say, a fact of the greatest practical importance, for it amounts to this: that we may often allow to those with very weak digestions foods which are generally considered indigestible, provided that they be thoroughly comminuted, whether by mastication or artificial means.