abundantly in the leaf, though the latter, of less agreeable flavor, has been little used, and is not in commerce. The use of the coffee-leaf is further discouraged by the fact that the plucking of the leaf is injurious to the crop of the berry.
The chemist also finds theine or caffeine in two South American plants, the maté and the guarana. The former, yerba maté, or "Paraguay tea" (Ilex Paraguayensis), is a small forest-tree, bearing fine white flowers, indigenous to Brazil and the Argentine Republic, where it has long been prepared for a beverage which is drunk throughout South America. The leaves and twigs are employed, sometimes with inclusion of the fruit. Brazil also furnishes guarana, an article known in medicinal commerce, and obtained from the seeds of Paulinia sorbilis, a climbing shrub. Its fruit is of the size of the grape, and has a single seed. The seeds are bruised into a pulp, molded into cylindrical cakes, and dried. So prepared, guarana is in habitual use in South America, infused as a beverage, and also taken solid as an adjunct to food.
One more plant has to be named as a source of theine—the tree of the cola-nut, of Western Africa (Cola acuminata). The tree, of which two varieties are found, one with broad and one with narrow leaves, has been cultivated somewhat in tropical countries. The nuts are of the size of a pigeon's-egg, of a brownish color, a fragrant odor, and aromatic, bitter taste. The natives prize them very highly, using them in the solid state as a condiment with food, and to sustain strength during continued exertion when the supply of food is deficient. The cola-nut is rich in theine, as first shown by the analysis of Professor Attfield, at London, 1864.
So far, then, only five plants on the globe have been found to contain the alkaloid theine or caffeine, but the chemist finds an alkaloid very closely allied to this one, though of distinct individuality, namely, theobromine. This interesting chemical compound is homologous with the alkaloid of tea and coffee, differing in the molecule by one atom of carbon and two of hydrogen, theine having the structure C8H10N4O2, and theobromine C7H8N4O2. The relation is the same as that between any two contiguous members of the methylic alcohol series. Theine is constituted as methyl-theobromine, C7H7 (CH3) N4O2, and the chemist finds it an easy task to change theobromine into theine. Now, theobromine can be artificially produced from xanthine (C5H4N4O2); indeed, theobromine is dimethyl-xanthine, and theine is trimethyl-xanthine. In other words, xanthine may be presented as a chemical ancestor of the active principle of tea and coffee, and so it becomes of interest to inquire into the origin of xanthine, so called. In reply, it must be said that xanthine is not found in plants, but it is found in chemical laboratories; it is not a myth, and it can be made from a good many things that are abundant on the face of the earth. It can be made from uric acid, and
