[49.] What are the uses of all these juices and secretions? To dissolve the food we eat.
a, the œsophagus or gullet; b, one end of the stomach; d, the other end joining the intestine; e, gall duct; f, the gall-bladder; g, the pancreatic duct; h, i, the small intestine.
We eat all manner of dishes, but in all of them that are worth eating we find the same kind of things, which we call food-stuffs.
We eat various kinds of meat; but all meats are made up chiefly of two things: the substance of the muscular fibre, which you have already learnt is a proteid matter containing nitrogen, and the fat which wraps round the lean muscular flesh. Now, proteids are, when cooked, insoluble in water (see p. 49); and fat, you know, will not mingle with water. Both these parts of meat, both these food-stuffs, must be acted upon before they can pass from the inside of the alimentary canal, through the epithelium of the mucous membrane, into the blood capillaries.
Besides meat we eat bread. Bread is chiefly composed of starch; but besides starch we find in it a substance containing nitrogen, exceedingly like the proteid matter of muscle or of blood.
Potatoes contain a very great deal of starch with a very small quantity of proteid matter; and nearly all the vegetables we eat contain starch, with more or less proteid matter.
Then we generally eat more or less sugar, either as such or in the form of sweet fruits. We also take salt with our meals, and in almost everything we eat, animal or vegetable, meat, bread, potatoes or fruit, we swallow a quantity of mineral substances, that is, various kinds of salts, such as potash, lime, magnesia, iron, with sulphuric, hydrochloric, phosphoric, and other acids.