EXPERIMENTS WITH OUR MUSCLES. 11 



9. Place the Land on tlie outside of tlie slioulder ; raise 

 tLe arm to a horizontal position ; repeat witli a weiglit in tlie 

 Land. 



10. Stand erect witli tlie Leels close to each other, but not 

 quite toucliing; let tlie arms Lang freely by tlie sides; rise .on 

 tiptoes, without moving otherwise ; repeat twenty times. 



11. Place tlie tips of tlie fingers on tlie angles of tlie lower 

 jaw ; shut tlie teetli firmly on a piece of rubber, and note tlie 

 bulging of tlie Masseter muscles. 



12. Press tlie fingers on tlie temples; again shut the jaw 

 firmly, and feel tlie action of the Temporal muscles. 



13. Make a narrow band of paper tLat will snugly fit tlie 

 forearm when the Land is open ; now clencL tlie fist strongly. 



14. Witli a tape-measure get tlie circumference of tlie up- 



Fig. 2. The Shortening and Thickening of the Biceps Muscle in raising the 

 Forearm. 



per arm when the arm Langs free ; again wLen tLe forearm is 

 strongly flexed. 



15. In tLe same way measure tLe forearm when the Land 

 is open, and wLen tLe Land is clenched. 



By these experiments we learn that when a muscle works 

 it becomes shorter, thicker, and Larder. 



