Stimulants — Tea and coffee contain an alkaloid theine, besides volatile oils, tannin, &c. Cocoa contains the milder alkaloid, theobromine. They stimulate the heart and nervous systems; tea and coffee have also a diuretic effect. Formerly they were erroneously thought to lessen tissue waste. These alkaloids, being purins, are open to the general objections named elsewhere. Stimulants do not impart energy or force of any kind, but only call forth reserve strength by exciting the heart, nervous system, &c.