THE MUSCULAK SYSTEM 79 



he is disabled from manual work requiring dexterity or 

 skill. Sometimes an additional glass of liquor seems 

 to steady the hand for a time, but tne shakiness soon 

 returns. 



104. Tobacco and other narcotics also affect muscular 

 activity through their effect upon the nerves. All nar- 

 cotics have as their natural, characteristic influence the 

 paralyzing of some of the nerve centers. As medicines 

 they may give relief from pain and so act beneficently 

 under skillful application. Tobacco has a special effect 

 upon the nerve centers regulating the action of the 

 muscles of the heart, making that action irregular and 

 less vigorous. This is particularly true of the young, and 

 it is not very uncommon for boys addicted to excessive 

 cigarette smoking to develop serious disease of the heart, 

 or even to die suddenly from " heart failure." Smoking 

 tobacco is found to interfere with work requiring fine and 

 delicate adjustment of muscular movement, as in watch 

 making and other delicate mechanical employments, in 

 scientific drawing, fine penmanship, etc. It is also for- 

 bidden to those persons in training for athletic contests, 

 and to all pupils in many schools, as well as to soldiers in 

 the armies of certain countries. 



DEMONSTRATIONS AND EXPERIMENTS 



17. General Structure and Properties of Muscles. It is important 

 that the pupils see muscles in their natural positions and connections. 

 For this purpose the frog is convenient, since the animal is so small 

 that little dissection is necessary, and since entire muscles can be 

 observed and owing to their great vitality can be made to perform 

 their natural movements. The frog should be pithed or decapitated, 

 and the skin removed from one of the hind legs. The muscles of 

 the limb then stand out distinctly (Fig. 7, p. 18). The belly of a 

 muscle can be distinguished from its tendinous ends, and the origin 



