Tea, in its chemical composition, is similar to coffee, containing even a greater percentage of the alkaloid caffein, and also a larger percentage of tannic acid. Tannic acid is present in larger quantities in green tea than in the black variety. In addition to the evil effects caused by the caffein which it contains, tea is more destructive to the normal activities of the stomach because of the tannic acid. The student may get some idea of what the stomach of the tea-user has to contend with, when it is stated that tannic acid gets its name from the essential action that this substance has in the process of tanning leather.