The ones that are in more or less universal use among civilized people are coffee, tea, and chocolate. Most of our coffee comes from Brazil, our tea from Japan, China, and India, and our chocolate from the West Indies. The use of caffeine-bearing parts of plants as beverages in various parts of the world has already been spoken of.

Coffee

The dried coffee-seeds are roasted and then ground before use. Roasted coffee contains 0.6 to 2 per cent. of caffeine, a small amount of caffeol (caffeon), and a large amount of tannic acid. Caffeol is an empyreumatic volatile oil (a mixture) developed in the roasting. It is the source of the flavor and aroma of the coffee, and is so penetrating that a single drop of it will fill a room with the coffee odor. The tannic acid of coffee, caffeotannic acid, unlike that of tea, does not precipitate albumin, gelatin, or alkaloids, and is not astringent. It is consequently of no use as a precipitant in poisoning by alkaloids. It constitutes undesirable extractive matter, however, in coffee, for so much colloid matter tends to check digestion and to retard absorption.

The beverage is prepared by pouring boiling water over freshly ground coffee and allowing it to steep for a few minutes; or by permitting boiling water to percolate through the ground coffee in a special coffee-pot. The coffee should not be boiled, as boiling drives off the flavoring volatile oil and makes a heavier decoction of the extractive matter.

Tea

This is made from the young leaves, which are prepared by a process of rolling, fermenting, and drying. The constituents are 1 to 4 per cent. of caffeine, a minute amount of theophylline, 0.6 per cent. of volatile oil, which imparts the flavor and odor, and a large amount of tannic acid of the kind that precipitates gelatine, albumin, and alkaloids, and is strongly astringent. India and Ceylon teas contain much more tannic acid than China teas (Luke). Green tea is made from the younger leaves. It contains more tannic acid, more volatile oil, and less caffeine than black tea, so is less stimulating and more astringent. In a number of samples Bannister found that the black teas averaged 3.24 per cent. of caffeine and 16.4 per cent, of tannic acid, while the green teas averaged 2.33 per cent, of caffeine and 27.14 per cent, of tannic acid. These figures do not correspond with those of Spencer, who found 4.8 to 15.8 per cent. of tannic acid in various teas. It is claimed that in the preparation of the tea leaves for the market about half the tannic acid is lost.

The beverage should be made by pouring boiling water upon the leaves and allowing them to steep from two to five minutes. The tea should not be boiled, as this hastens the solution of the tannic acid and drives off the flavoring oil. As the tannic acid and coloring-matter dissolve but slowly in water that is not boiling, a fair percentage of these may be left behind if the tea is soon poured off the leaves. If it is allowed to steep too long, the beverage becomes more deeply colored and richer in tannic acid. The tea which stands all day long in the tea-pot and is drunk cold by the inveterate tea-drinker is essentially a solution of tannic acid which would effectively tan hides into leather.

The amount of tea used in making a cup represents 1 to 2 grains (0.06-0.12 gm.) of caffeine, and the coffee per cup 1 1/2 to 3 grains (0.1-0.2 gm.), but always some of the caffeine is left behind. Tea leaves contain more of the caffeine than coffee, but much less tea is used per cup.

Pharmacologic Action

Besides the caffeine action, coffee derives some of its properties from the empyreumatic oil, caffeol. This is somewhat stimulating to the cerebrum, but in the alimentary tract is a local irritant. Pincussohn has found that coffee results in a prompt increase in the amount and the acidity of the gastric juice; and it is a well-known fact that on the intestines the beverage acts as a laxative, promoting peristalsis. These factors may not be of importance in normal persons, but they become so in hyperesthetic states of the stomach (hyperchlor-hydria, hypersecretion, and gastrosuccorhea) and in diarrhea, so that coffee may be contraindicated.

Tea seems to have a more immediate stimulating effect, either because of its volatile oil or because absorption is more rapid. In "strong" tea the local action in the alimentary tract is due chiefly to its tannic acid. This tends to lessen gastric secretion, to retard absorption, and to induce constipation, so that tea which is strong in tannic acid may decidedly interfere with digestion. But because it contains less extractive matter than coffee, properly made tea - i. e., tea without much tannic acid - is less disturbing to the stomach than coffee. In nervous dyspepsia both tea and coffee are harmful because of the caffeine effect on the nervous system.

Coffee and tea are not nutritive in themselves, and require no digestive process for their absorption. But the addition of milk or cream and sugar changes them into food. In tea the tannic acid precipitates the coagulable protein of the milk, but this precipitate digests in the gastric juice. In some instances the milk and cream have a desirable effect by lessening the local irritant action in the stomach, and by retarding the absorption of the caffeine.

As therapeutic amounts of caffeine are directly antidotal to the cerebral effects of alcohol, the after-dinner demi-tasse may have a special use when wine has been drunk at the dinner. As a hot drink which contains a volatile oil it may also be slightly stimulating to the stomach. However, its reputation as an aid to digestion depends more on habit than upon any intrinsic power in the stomach.

The coffee and tea habits are common among brain-workers (students, writers, etc.) and those who must remain awake at night (nurses, journalists, etc.). The tea habit is prevalent in some localities, the afternoon "cup that cheers but not inebriates" being employed to brighten the gossip of an afternoon call or to remove the feelings of tiredness. In the southern United States the "kola habit" is prevalent, a proprietary drink being in great favor. Much coffee or tea may result in nervousness and insomnia, with cardiac and digestive neuroses; but in such a case stoppage of the beverage will usually be sufficient to restore the patient to normal in a short time. (See Chrome Caffeine Poisoning, p. 262.) In insomnia caffeine drinks must not be taken late in the day.

Tolerance

The variations in individual susceptibility to tea and coffee are marked, one person being wakeful and restless and mentally stimulated by a single cup of coffee or tea, while another will be unaffected by several cups. In many instances a limited toleration is set up, so that the amount of tea or coffee may be steadily increased for a time; but it is an interesting fact that long-continued excessive drinking of tea or coffee sometimes results in a condition of increased susceptibility which may persist for months or even years. So that one who formerly regularly drank several cups of coffee a day with apparent impunity finds himself unable to drink more than one or two cups without feeling the bad effects. The habitual cup of coffee or tea seems to have little if any diuretic effect.

The drinking of tea and coffee is so common, and their harmful effects are so evident, that physicians are prone to proscribe these beverages rather than to prescribe them.

Before leaving this subject I should like to say to every student that if he gets into a state in which night after night he cannot work without coffee, he is drawing upon his reserves, so that when he needs to make a spurt he will be unable to do so. In such a case what he really needs to clear his brain is a short period of rest from excessive study, with open-air exercise and good sleep. If he is to have some special test of his knowledge, such as an examination, then a cup or two of coffee may enable him to do his best intellectual work, while an excessive amount will only make him nervous and unable to think clearly.

Chocolate

Chocolate is the paste made from the ripe seeds of the chocolate plant, Theobroma cacao, after they have been sweated, dried, roasted, and deprived of their shells (the so-called "cocoa nibs")- The sweating or fermentation process removes practically all the tannic acid and some of a bitter substance which is present in the ripe seed, and the roasting brings out the chocolate flavor. Chocolate contains from 0.3 to 2 per cent. of theobromine (according to some authorities, also caffeine up to 0.35 per cent.), 10 per cent. of starch, 15 per cent, of vegetable protein, and 30 to 50 per cent. of a peculiar fat which is known as cocoa-(cacao) butter. (See Fats, Part I.) Pure chocolate is not pleasant to the taste, so for eating and drinking it is regularly sweetened with sugar and often flavored with vanilla. It is highly nutritive, and has been shown by Weissmann, Zuntz, and others to be almost completely digestible, but the fat acts in the stomach to retard both the secretion of gastric juice and the motor functions, i. e., the emptying of the stomach, so chocolate cannot be taken in large quantities. Neumann replaced a fixed allowance of bread, sausage, pork, sugar, and cheese with an amount of cocoa and cocoa-butter of equal caloric value. The diet was moderately satisfactory, but he developed a severe headache which he attributed to the theobromine.

Cocoa is a powdery preparation, made from chocolate by removing a portion of the cocoa-butter by hydraulic pressure, with or without heat. The dried residue is ground to a very fine powder, so that it may be more readily mixed with water. The proportion of the theobromine in cocoa is thus somewhat higher than in chocolate, while the fat is less, constituting only 15 to 30 per cent. Inferior cocoas are made by diluting the chocolate with starch, thus reducing the theobromine as well as the fat. The so-called Dutch process is one of partial saponification of the fat with an alkali, to make it miscible with water.

The beverage "cocoa" is made by boiling the cocoa powder with water or milk for at least five minutes, so that its starch may be properly hydrolyzed; otherwise it is nothing but a crude mixture from which the powder tends to separate. When it is made with milk and is sweetened with sugar, it has a high food value; a cupful of such a beverage, prepared with about 10 grams of cocoa, giving a nutritive value of perhaps 250 calories. Such a drink may sometimes be taken by invalids for its food value.

Chocolate is sometimes made into a beverage, but it contains so much fat and requires so much sugar that it is rich and sweet and is heavy in the stomach. It is not suited for invalids.

Cocoa and chocolate have the properties of theobromine, but kidney tolerance is soon established, so that no "diuresis" results from the habitual cup.