THE FOOD AND DIGESTION 383 



holism, along with its influence in producing dilatation of 

 the cutaneous vessels, is taken advantage of in its use in 

 the treatment of high temperature in some fevers. 



Tea, Coffee, and Cocoa have as their essential constituents 

 the substances theine and caffeine, which are methyl deriva- 

 tives of xanthin, a diureide which is excreted in the urine 

 (see p. 397). They tend to paralyse the sensory mechanism 

 of the brain, and hence abolish the sense of fatigue. They 

 stimulate the heart and the secreting action of the kidneys, 

 but they have no effect upon the metabolism. Cocoa nibs 

 contain about 8 per cent, of proteid and about 50 per cent, 

 of fat. Cocoa is therefore an energy -yielding food. 



