A feebly basic alkaloid obtained from the dried leaves of Thea sinensis or from the dried seeds of Coffea arabica and also found in other plants. Tea contains from 1 to 4 per cent, of caffein; coffee from 1 to 2 per cent.

Properties : Caffein is trimethyl-xanthin. It occurs as white silky glistening needles, usually matted together in fleecy masses, odorless and having a bitter taste. It is soluble in water (1 :50) and in alcohol (1 :50). The solubility in water is materially increased by the addition of sodium benzoate or sodium salicylate.

Action and Uses: Small doses of caffein act on the nervous system, stimulating the psychic centers, the respiratory and vasomotor centers and the reflexes. It modifies the circulation by stimulating the heart, and relaxing the vessels by direct action. The flow of urine is increased. Muscular contraction is facilitated and fatigue lessened. Excessive doses produce insomnia, nervousness, headache, palpitation and nausea or vomiting, especially in susceptible persons. They lessen the capacity for mental or muscular work. Toxic doses may produce tetanic convulsions and cardiac dilatation.

CIRCULATION: Caffein has a rather complex and, therefore, somewhat inconstant action. In therapeutic doses the pulse may be quickened or slowed. The blood-vessels tend to dilate by the peripheral action and to contract by the central action. The dilatation probably predominates in most cases, but the blood-pressure rises slightly by increased force and output of the heart. This increased output and lessened resistance tend to produce a more rapid flow of blood, and this results in an increased flow of urine. These effects make caffein especially efficient in some cases of cardiac dropsy, although it is generally inferior to digitalis. The cardiac stimulation is also useful in temporary cardiac weakness.

By the Germans, and by many physicians in this country, caffein is looked on as the most valuable drug for the treatment of circulatory failure in acute infectious processes, such as pneumonia, peritonitis, scarlet fever, etc.

A disadvantage in the use of large doses is the cerebral stimulation produced, which often prevents sleep. Some authors do not approve of the use of caffein as a cardiac remedy, but believe that its utilities are confined to its diuretic action.

Caffein is used as a nervous stimulant in cases of nerve exhaustion. It is useful in collapse by causing rise of blood-pressure and stimulating the respiration. It may be-used in narcotic poisoning in the form of hot coffee, or by itself, for its effect on the respiratory system. It is especially useful in opium poisoning, and it may be used in alcoholic poisoning on the same principle. It relieves some forms of headache, but in the congestive form it may increase the difficulty. It is excreted by the kidney partly under its own form, partly as mono- or dimethyl-xanthin. It does not increase the amount of uric acid in the urine.

Dosage: The dose of caffein varies from 0.06 gm. to 0.3 gm., or about 1 to 5 grains. When given in the form of coffee a cup made from a tablespoonful (15 gm.) would contain from 0.1 to 0.2 gm. or from 1 to 3 grains.

The alkaloid may be given in the form of powder or in capsules or cachets. In combination with equal parts of sodium benzoate or sodium salicylate it dissolves readily, and may be given hypodermically or administered by mouth.