The most important of these are water; common salt; and the chlorides, phosphates, and sulphates, of potassium, magnesium, and calcium. A sufficient quantity of most of these substances, or of the material for their formation, exists in all ordinary articles of diet, so that we do not swallow most of them in a separate form. Water and table salt form exceptions to the rule that inorganic bodies are eaten imperceptibly along with other things, since the body loses more of each daily than is usually supplied in that way. It has been maintained that salt as a separate article of diet is an unnecessary luxury, and there seems to be some evidence that certain savage tribes live without more than they get in the meat and vegetables which they eat. Such tribes are, however, said to suffer especially from intestinal parasites; and there is no doubt that to many animals as well as most men the absence of salt from their diet is a terrible deprivation. Buffaloes and other creatures are well known to travel miles to reach " saltlicks;" of two sets of oxen, one allowed free access to salt, and the other given none save what existed in its ordinary food, it was found after a few weeks that those given salt were in much better condition. In man the desire for salt is so great that in regions where it is scarce it is used as money. In some parts of Africa a small quantity of salt will buy a slave, and to say that a man commonly uses salt at his meals is equivalent to stating that he is a luxurious millionaire. In British India, where the poorer natives regard so few things as necessaries of life that it is hard to levy any excise tax, a large part of the revenue is derived from a salt tax, salt being something which even the poorest will buy. As regards Europe, it has been found that youths in the Austrian empire who have fled to the mountains and there led a wild life to avoid the hated military conscription, will, after a time, though able abundantly to supply themselves with other food by hunting, come down to the villages to purchase salt, at the risk of liberty and even of life.

What is the chief source of carbohydrates? Name the most important. Name carbohydrate foods derived from animals. How do they resemble fats in composition, and how do they differ from them? Can an ounce of starch yield as much energy to the body as an ounce of fat? Give a reason for your answer.

Name the more important inorganic foods. Why do we not require to eat most of them separately ? What inorganic foods are taken in a separate form ? Why ?