44 EXPERIMENTAL PHYSIOLOGY. 



rhythmic movements are superimposed upon whatever condition 



of tone prevails. 



The intrinsic nerve supply seems to preside over rhythmicity. 



Experiment 16. Contraction of Smooth Muscle. An L- 

 shaped glass rod is fastened by a clamp so that it can be used 

 to support a piece of intestine about 2 cm. long in a small beaker 

 of Ringer's solution. The latter is maintained at a tempera- 

 ture of 37-38 C. by immersing the beaker in a large tin cup 

 used as a water-bath. Air is allowed to bubble slowly through 

 the Ringer's or Locke's solution 1 by fixing a small glass tube, 

 connecting with the compressed air supply, so that its opening 

 is near the bottom of the beaker. When all is ready one end 

 of a piece of intestine, cut from a rabbit which has just been 

 killed, 2 is attached to the hook of the glass rod and the other 

 to a heart-lever which is arranged to record on a slowly-moving 

 drum. Contractions of the longitudinal muscle will produce 

 movement of the lever. 



After recording several normal contractions try the effect 

 of temporarily reducing the air supply. Later allow the tem- 

 perature of the Ringer's fluid to fall to that of the room and note 

 the changes in tone and rhythmic contractions. Finally study 

 the effect of stimulation by electricity. When ready to stimu- 

 late remove the Ringer's solution for a short time in order to 

 prevent short circuiting. Try make and break, direct and 

 indirect currents. Later attempt to tetanize the segment. 

 On account of the long latent period do not run the stimuli too 

 close together when single shocks are used. 



Observe the direction in which a contraction travels when a 

 piece of intestine is pinched with forceps. In order to remember 

 which is the oral end a ligature should be tied around that end 

 when the segment is removed. Do the contractions always 

 move in the same direction from mechanical stimulation? Is 

 this type of stimulus more or less adequate than the electrical? 



water with which these solutions is made up must be pure distilled. It 

 has been our experience in this laboratory that chlorinated lake water cannot be 

 used to distil from. We are compelled to use spring water from which to pre- 

 pare the distilled water. 



2 The intestine, after removal from the rabbit, is preserved in cold Locke's 

 solution through which oxygen or air is occasionally bubbled. 



