A CLEAR MIND THE NEED OF THE DAY 329 



by the rapid multiplication of those which remain. Man is, 

 however, learning to fight them more and more successfully. 

 Microscopes are discovering where they are, and careful 

 scientific studies are showing how in a measure they may be 

 avoided. Indeed, through modern sanitation, which has 

 driven them backward and has reduced the number and 

 violence of epidemics, men have succeeded in making the city 

 almost as secure against microbes as the country. We shall 

 notice in another chapter some of the methods adopted today 

 in fighting this worst enemy in our struggle for existence. 



THE USE OF DRUGS THAT AFFECT THE BRAIN 



Another enemy against which man has to contend is 

 especially dangerous because it also is not commonly recog- 

 nized as a foe. Indeed, many people look upon it as a friend, 

 while others regard it as a luxury, which may be indulged in 

 more or less frequently without thought of danger. The 

 nervous system controls the whole body, and everything that 

 affects the activities of the brain has a profound influence upon 

 the whole life. But some men have unfortunately developed 

 the habit of using certain substances which have a direct 

 action on that organ and interfere with its normal functions. 

 There are two classes of brain drugs: stimulants, and nar- 

 cotics each of which has pernicious effects. 



Stimulants. There is great difference of opinion as to the 

 proper definition of the word stimulant. This term usually, 

 however, denotes a drug that will excite an organ to increased 

 activity. The effect is temporary and does not indicate in- 

 creased strength, but only enables the body to call upon its 

 reserve power a little more quickly. In most cases, if not in 

 all, the stimulating action is followed by a corresponding 

 depression so that there is no gain in the end. A whip gives 

 no power to a jaded horse, though it may excite him for a 

 short time to more exertion. The constant use of a stimu- 

 lant, too, acts somewhat like the constant use of a whip on a 



