LABORATORY MANUAL OF PHYSIOLOGY. 



When the weight is supported by the muscle, only during the period 

 of contraction, the muscle is said to be after-loaded. Compare the 

 muscle curves obtained with load and after-load, using first small 

 weights and then heavier and heavier weights. 



XI. EFFECT OF TEMPERATURE UPON THE MUSCLE CURVE. 



For the study of the effects of changes of temperature upon the 

 muscle curve, the muscle warmer of Porter is very convenient. 

 Where this is not at hand, the same results may be obtained by the 

 use of a bath of physiological salt solution, which may be cooled or 

 heated to the desired temperature and in which the muscle may be 

 immersed, except for the short period required for stimulating and 

 recording contractions. 



1. Place the musde in a small test tube surrounded by an ice 

 pack until the temperature of the interior of the tube has fallen to 

 zero or less, i.e., until the freezing point has been reached. Re- 

 move the muscle and record a single twitch. Label the tracing. 



2. Warm the muscle to 5 Centigrade and again record a twitch. 



3. Warm the muscle to 10 C. and again record. 



4. Warm to 15 C. and record again. 



5. Warm to 20 C. and repeat record. 



6. Warm to 30 C. and record again. 



7. Warm to 40 C. and record again. 



8. Bathe the muscle with salt solution heated to 45 C. and note 

 result. The muscle passes into rigor. 



Compare the curves obtained at the different temperatures and 

 tabulate your results. WTiat is the effect on the height of contrac- 

 tion ? On the time of the contraction phase ? On the relaxation 

 period? 



XII. INFLUENCE OF FATIGUE ON THE FORM OF THE SINGLE 

 MUSCLE TWITCH. 



i. Set up the apparatus for automatic stimulation of the muscle 

 or nerve as shown in Fig. n. Make a sciatic-gastrocnemius 

 preparation. Arrange the inductorium for maximal stimulation. 



[26] 



