CHEMICAL INJURY TO THE NERVOUS SYSTEM 255 



the usual drink, it acts as a mild stimulant, increasing the 

 heart action. The chief danger in coffee- or tea-drinking lies 

 in the fact that one may come to depend upon it as a regular 

 heart stimulant. In that case one comes to require ever- 

 increasing amounts and to feel weak and helpless without it. 

 There is no excuse for children's drinking coffee. 



The action of caffein resembles the action of nicotin and 

 alcohol in that the reaction counterbalances the first gain. 

 The stimulation is followed by a period of depression, just 

 as in the case of nicotin the narcotic effect is followed by a 

 period of irritation or restlessness. Again, as the protoplasm 

 becomes more and more familiar with the alkaloid, a larger 

 quantity of the latter is required to produce a given amount 

 of stimulation. Finally, as in the case of tobacco and alcohol, 

 though probably not so quickly, the continued use makes one 

 feel that he cannot be comfortable without it. 



These consequences are not observed with ordinary foods, 

 but they are observed with all the drugs. 



Tea leaves contain, in addition to the stimulating alkaloid and 

 the aromatic oil that gives the flavor to the drink, a considerable 

 quantity of tannin. This substance combines with proteins to form 

 a hard, tough substance, and is thus used in the tanning of leather. 

 If tea leaves are allowed to stand in the water too long, the tannin 

 becomes dissolved. It is this that makes strong tea pucker the lips 

 and the inside of the mouth. Habitual drinking of strong tea will 

 in the same way pucker the lining of the stomach ; as the tanning pro- 

 ceeds, the stomach lining becomes hardened, and digestion may 

 thus be interfered with. 



308. Habit-forming drugs. A large number of plants that 

 were formerly used as medicaments have been carefully studied 

 in recent years, and the active substances have been separated 

 out in a pure state. In this way we have become acquainted 

 with several important substances, which are very useful in 

 the hands of the expert but very dangerous in the hands of 

 the ignorant. 



