The tongue is simply a "tongue-shaped" bundle of muscles, covered with a thick, tough skin of mucous membrane, dotted all over with little knob-like processes called _papillae_, which are of various shapes, but of no particular utility, except to roughen the surface of the tongue and give it a good grip on the food. If the mucous "skin" covering the tongue does not shed off properly, the dead cells on its surface become thickened and whitish, and the germs of the mouth begin to breed and grow in them, forming a sort of mat over the surface. Then we say that the tongue is badly coated. This coating is in part due to unhealthy conditions of the stomach and bowels, and in part to lack of proper cleaning of the mouth and teeth. The Sense of Taste can usually be Trusted. Since the nose and the tongue have had about five million years' experience in picking out what is good and refusing what is bad, their judgment is pretty reliable, and their opinion entitled to the greatest respect. As a general thing, those things that taste good are wholesome and nutritious; the finest and most enjoyable flavors known are those of our commonest and most wholesome foods, such as good bread, fresh butter, roast meats, apples, cheese, sugar, fruit, etc.; while, on the other hand, those things that taste bad or bitter or salty or sour, or that we have to learn to like, like beer or pickles or strong cheese or tea or coffee, are more often unwholesome or have little nutritive value. Very few real foods taste bad when we first try them. If we used our noses to test every piece of food that went into our mouths, and refused to eat it if it "smelt bad," we should avoid many an attack of indigestion and ptomaine poisoning. It is really a great pity that it is not considered polite to "sniff" at the table. THE EYE How the Eye is Made. Next in importance after the smell and the taste of our food comes the appearance of it; hence, our need of eyes to help us in choosing what to eat, as well as how to avoid the dangers about us. The eyes began as little sensitive spots on the surface of the head. Like the nose pits, as they became more sensitive, they too sank in beneath the surface; but with this difference, that, instead of remaining open, the rims or edges of the eye-pit grew together and became transparent, forming a cover, or eye-glass, which became the clear part of the eye, called the _cornea_. At the same time, the little sensitive spot at the bottom of the eye-pit spread out into the shape of the bottom of a cup, called the _retina_; and then the hollow of that cup between the retina and the cornea filled up with a clear, soft, animal jelly called the _vitreous humor_, and we have the eye as it is in our heads to-day. The sensitive retina, spreading out, as it does, to form the back of the eyeball, is the nerve-coat of the eye; and from its centre a thick round bundle of nerve fibres, known as the _optic nerve_, runs back to the brain.