290 THE HUMAN MECHANISM 



just as truly as there are slaves of tobacco, or of alcohol, 

 or of opium. It is worse to be the slave of alcohol than of 

 coffee, because the evil consequences of alcohol are greater 

 than those produced by the corresponding use of coffee; 

 but it is by the same process in both cases that the man 

 or woman becomes a slave to the drug, and that process is 

 the formation of bad habits. 



With these practical considerations about the use of drugs 

 by which term it will be seen that we mean not simply 

 the medicines purchased from the apothecary but all those 

 substances which are taken into the body in order to give 

 some new or abnormal direction to the course of events in 

 the organism we may pass on to the discussion of those 

 in common use. 



4. Tea and coffee. Different as are these drinks in taste 

 and appearance, their most important physiological effects 

 are due essentially to the same substances ; namely, caffeine 

 (or theine) and tannic acid (or tannin). Caffeine is a very 

 powerful stimulant, especially of the nervous system and 

 also of the heart, although probably to a lesser degree ; 

 tannin, on the other hand, is a bitter, astringent substance, 

 which may considerably hinder digestion and directly injure 

 the mucous membrane of the stomach. Tea contains about 

 twice as much tannin as an equal weight of coffee, but as 

 coffee is frequently made much stronger than tea, the actual 

 amount per cup may often be more nearly equal in the two 

 drinks than these figures indicate. The amount of tannin 

 dissolved in tea varies greatly with the method of prepara- 

 tion, and largely for this reason tea should not be boiled 

 nor allowed to steep too long. The proper method of making 

 tea is to pour over the dry leaves water which has been 

 brought just to the boiling point and then to allow the 

 infusion to stand, without further heating, for not more 

 than a few minutes. 



Both tea and coffee seem to have a slightly retarding 



