LESSON VII. ACTION OF SOME CHEMICAL 

 SUBSTANCES ON NERVE AND MUSCLE. UN- 

 STRIATED MUSCLE. 



1. Muscles may contract in two ways under the in- 

 fluence of drugs. There may be a series of brief quick 

 contractions (twitchings) like those caused by induction 

 currents, or there may be a slow gradual contraction 

 somewhat like the protracted contraction caused by the 

 galvanic current, lasting a relatively long period, and 

 in some muscles lasting for hours. In some cases the 

 contraction is caused by an action on the nerve ending 

 or on the small part of the muscle immediately under 

 it; in other cases it is caused by an action which may 

 occur at any part of the muscle fibre. Curari stops the 

 former but does not stop the latter. The following ex- 

 periments will illustrate these points. 



2. Protracted contraction caused by nicotine. 

 This is best seen in the rectus abdominis muscle of the 

 frog. It occurs to a greater or less extent in the other 

 muscles of the frog, but is not known to occur in the 

 mammal. 



Expose the rectus abdominis muscle in a frog im- 

 mediately after death; gently press the surface of the 

 muscle with blotting paper to remove excess of fluid, 

 and draw a fine brush moistened with -01 p.c. nicotine 

 transversely across the middle of a muscle segment, the 

 segment will slowly contract. 



Expose the thoracic muscles, blot, place a drop about 

 1 mm. in diameter on the end of one of the muscles 



