197- Heat ric/or. Using the muscle of the la>t experiment, dis- 

 connect the inductcrium and attach to the signal magnet wires from 

 the desk binding posts which will give time intervals of 15 seconds. 

 Revolve the drum very slowlv and at the same time raise the 

 temperature of the "muscle warmer" about one degree in 2 minutes. 

 Mark on the rigor curve thus obtained the temperatures. Note 

 especially the temperature at which marked shortening or heat 

 rigor of the muscle begins. 



198. Action of salt-solutions on muscle. a. Use curarized 

 muscles. Remove small muscles ( sartorius, biceps, tibialis, etc.) 

 from the leg of the frog, with as little injury as possible, and place 

 in the following solutions, which should be cJuuujcd two or three 

 tunes to remove all foreign substances. 



a. m/ 4 sugar solution (non-electrolyte). 



b. Mixture of 4 vols. 111/4 sugar -)- i vol. m/8 NaCl. 



c. m/8 NaCl pure. 



d. m/8 NaBr pure. 



e. m/8 NaXO 4 (calcium precipitant). 



f. .Mixture of 24 vols. m/8 NaCl + I vol. m/8 CaCl,. 



g. m/8 KC1 pure, 

 h. m/8 CaCl., pure. 



Note the following points : ( i ) Any immediate change on placing 

 the muscle in the solution; (2) behavior of the muscle after it has 

 been in the solution for several minutes; (3) changes in the irrita- 

 bility of the muscle : test with single induction shocks at ten-minute 

 intervals. 



(a) Which solutions cause the muscle to contract or shorten 

 permanently ? 



(b) Which produce rhythmical contractions or twitches? Which 

 do not? Which solutions have the greatest effect of this kind? 



(c) Which solutions deprive the muscle of irritability most 

 rapidly ? Compare especially solutions a and b. 



b. After irritability has disappeared try the effect of transferring 

 the muscle to normal saline solution ( NaCl in tap water). Does the 

 irritability return? 



c. Compare the behavior of the muscle in m/8 NaCl, m/8 Nal'.r, 

 m/8 Na,SO 4 . Any difference? Then try the effect of adding to 

 each solution a few drops of m/8 CaCl., What is the effect? What 

 do you conclude from this experiment and from the action of 

 solution f above, as to the influence of Ca on the spontaneous activ- 

 ity of skeletal muscle? Try returning the muscle after an interval 

 to the pure m/8 NaCl, etc. Does the former behavior return? 



55 



