_Mastication, by breaking the food up into small particles, enables it to be brought into intimate contact with the digestive juices._--Such comminution is especially needful in the case of raw vegetable foods of the tougher kind, in order to break up their cellulose framework, and to set free the contained starch, proteids, and fats. Foods of this kind, unless masticated, yield practically no nutriment to the organism. I cannot too strongly emphasise the fact that before man learned to break up the cellulose framework of his vegetable food by cooking he was compelled to subject it to laborious mastication. But, while thorough comminution is especially needed for vegetable food when raw, it is also needed for many cooked forms of it also,--as, for example, solid batter pudding and new underbaked bread, heavy lumps of which, passing into the stomach, may seriously hamper the work of that organ. Such substances are indigestible essentially by virtue of their impermeability to the digestive juices, and they gain in digestibility in proportion as they are comminuted. The indigestibility of new bread would appear to be wholly due, not to any peculiarity of chemical composition, but to its tendency to elude the teeth and form a sodden mass impermeable to the digestive juices, while the more powdery stale bread is more easily broken up both in the mouth and within the stomach. Cabbage, again, owes its indigestibility to the fact that it is allowed to pass into the stomach in large masses, while the well-known digestibility of cauliflower and minced spinach is due to the fineness of their division; were cabbage as finely minced as spinach usually is it would be equally digestible.