i 4 o TEXT-BOOK OF PHYSIOLOGY. 



is made.^Inasmuch as tannin also coagulates peptones, the excessive 

 use of tea as a beverage is apt to derange" the 'digestive organs and 

 the general process of digestion^ 



Cocoa is more nutritive than either coffee or tea, on account of the 

 large amount of fat and proteid it contains. It is, however, less 

 stimulating. 



The active principles in coffee, tea, and cocoa, and to which their 

 effects are to be attributed, are caftein, them, and theobromin respec- 

 tively. These alkaloids are chemically closely related one to the 

 other and to the compound xanthin. They are present in the coffee 

 seeds, the tea leaves, and the cocoa bean to the extent of 1.7 per cent., 

 1.4 per cent., and 1.6 per cent, respectively. When prepared as a 

 beverage, however, there is three times as much caffein in coffee 

 as thein in tea. 



Alcohol when taken in small quantities stimulates the digestive 

 glands to increased activity and thus promotes digestive power. Its 

 absorption into the blood is followed by increased action of the heart, 

 dilatation of the cutaneous blood-vessels, a sensation of warmth, 

 and an excitation of the brain. In large quantities it acts as a paralyz- 

 ant, depressing more especially the vaso-constrictor nerve-centers and 

 certain areas of the brain, as shown by an impairment in the power of 

 sustained attention, clearness of judgment, and muscle coordination. 



Alcohol is undoubtedly oxidized in the body, as only about 2 

 per cent, can be obtained from the urine and expired air. It thus 

 contributes to the store of the body-energy. As to whether for this 

 reason it can be regarded as a food, that is, whether it can be sub- 

 stituted in .part at least for fat or carbohydrate material without im- 

 pairing the proteid metabolism, is at present a subject of experimen- 

 tation and discussion. According to some investigators, alcohol does 

 not retard proteid metabolism, for when it is introduced into the body 

 in amounts equivalent to the carbohydrates withdrawn from the food 

 there is at once a rise in the amount of nitrogen excreted. Hence it 

 cannot be regarded as a food. According to other investigators, 

 alcohol retards or protects proteid metabolism just as effectually as 

 an equivalent amount of starch or sugar. Many more experiments 

 are required to decide this question. When taken habitually in large 

 quantities, alcohol deranges the activities of the digestive organs, 

 lowers the body-temperature, impairs muscle power, lessens the 

 resistance to depressing external conditions, diminishes the capacity 

 for sustained mental work, and leads to the development of structural 

 changes in the connective tissues of the brain, spinal cord, and other 

 organs. In zymotic diseases and in cases of depression of the vital 

 powers it is most useful as a restorative agent. 



