LESSON VI. ACTION OF SOME CHEMICAL 

 SUBSTANCES AND OF TEMPERATURE ON MUSCLE. 



1. In a recently killed frog make the following pre- 

 parations and place them in Ringer's fluid : 



a. Cut through the tissue on either side of the lower 

 tendon of the sartorius muscle (Fig. 6). Pass a thread 

 under the tendon, tie and cut the tendon near the knee 

 joint. Hold up the end of the muscle by the thread, and 

 with fine pointed scissors cut through the connective 

 tissue on either side and below it, so that the muscle is 

 freed up to the pelvis. Cut away the muscles covering 

 the upper attachment, and cut the sartorius as close as 

 possible to the bone. 



b. Prepare similarly the sartorius of the opposite side, 

 but tie it at the pelvis instead of cutting it. Tie loops in 

 the threads at such distance as is suitable for fixing the 

 muscle in the moist chamber (cp. p. 24). 



Instead of tying the upper end, it is better to cut through the 

 pelvis in the middle line, and to cut away all the muscles except the 

 sartorius so that the muscle is obtained attached to the bone. 



c. Make a sciatic gastrocnemius preparation. 



2. Action of salts. When a muscle is placed in pure 

 NaCl solution, Ca salts diffuse out of it, and if the 

 former is approximately isotonic with blood plasma, 

 spontaneous contractions (twitchings) occur. The time 

 before they begin and their duration varies in different 

 muscles; in the sartorius of the frog they usually begin 

 in a few seconds and go on for several hours. The addition 



