552 APPLIED BIOLOGY 



The direct effect of tobacco is narcotic, and many smokers 

 say that it " soothes their nerves." It is very doubtful 

 whether the nerves would need " soothing " if the tobacco 

 habit had not been established. Opium also has such an 

 effect ; but it is well known that the craving for the soothing 

 is the result of the established habit, and those who never 

 used opium do not need to be soothed by that drug. Like- 

 wise those who have never acquired the tobacco habit appear 

 to have no need for its narcotic or soothing effect. The 

 difference between the opium and tobacco habits is in degree, 

 not in kind. Both create a demand or craving for their 

 peculiar narcotic effects. 



Some few people have their eyes seriously affected by even 

 small amounts of tobacco, while many find that tobacco 

 smoke irritates the eye-membranes and causes some blurring 

 of vision. 



The whole physiological truth about tobacco so far as now 

 known is that : (1) no one needs it except to satisfy an estab- 

 lished habit ; (2) many adults are injured by it, and no one 

 knows just how much will do harm to a particular person; 



(3) some adults are apparently not harmed by limited use ; 



(4) it is decidedly injurious to growing boys ; (5) those who 

 avoid establishing the habit in youth do not as a rule care to 

 learn later, for there are no physiological reasons why any one 

 should deliberately set out to learn the use of tobacco in any 

 form. 



480. Effects of Tea, Coffee, and Cocoa. The first two 

 are most important because they are so widely used as 

 beverages. It is now well known to physicians that many 

 people drink too much tea and coffee, and that temperance 

 is needed in use of these beverages no less than with alcoholic 

 drinks. Their stimulating effect is due to the presence of a 

 powerful drug (caffein), which has a stimulating action on 

 the nervous system. Nervousness, insomnia, headache, 

 and indigestion are common symptoms arising from exces- 



