Effects of Tea, Coffee, and Cocoa. Though the flavors of tea, coffee, and cocoa are so different, they all depend for their effect upon a spicy-tasting substance, called caffein from its having been first separated out of coffee. The caffein of tea is sometimes called _thein_, and that of cocoa _theobromin_; but they are all practically the same substance. Part of the taste of these beverages is due to the caffein, but the special flavor of each is given by spicy oils and other substances which it contains. Caffein acts as a mild stimulant both to the nervous system and brain, and to the heart; as is shown by the way in which tea or coffee will wake us up or refresh us when tired, or, if drunk too late at night, keep us from going to sleep. If used in large amounts, especially if taken as a substitute for food, tea and coffee upset the nervous system and disturb the heart, and produce an unwholesome craving for more. [Illustration: A MILK STATION IN A CITY PARK Many cities have established such stations, where people can buy, for a cent or two, a drink that is far better than soda water or any other beverage.] Their chief value lies in the hot water they contain, which has been sterilized by boiling, while its heat assists the process of digestion; and in the fact that their agreeable taste sometimes gives us an appetite and enables us to eat more of less highly flavored foods, like bread, crackers, potatoes, or rice, than we would without them. They are, also, usually taken with cream, or milk, or sugar, which are real foods and bring their fuel value up to about half that of skimmed milk. So far as they stimulate the appetite and increase the amount of food eaten, they are beneficial; but when taken as a substitute for real food, they are most injurious. A cup of coffee, for instance, makes a very poor breakfast to start the day on; for although it gives you a comforting sense of having eaten something warm and satisfying, it contains very little real food, and soon leaves you feeling empty and tired; just as an engine would give out if you put a handful of shavings into its fire-box, and expected it to do four hours' work on them. The most disturbing effects of tea and coffee upon the digestion are due to the tannin which they contain if boiled too long, especially in the case of tea. This tannin, fortunately, will not dissolve in water except by prolonged boiling or steeping; so that if tea is made by pouring boiling water over the tea leaves and pouring it off again as soon as it has reached the desired strength and flavor, and coffee by being just brought to a boil and then not allowed to stand more than ten or fifteen minutes before use, no injurious amounts of tannin will be found in them. Tea, made by prolonged stewing on the back of the stove, owes its bitter, puckery taste to tannin, and is better suited for tanning leather than for putting into the human stomach.