42 ELEMENTARY PHYSIOLOGY. VI. 



key in the secondary circuit. Note the slow relaxation 

 of the veratrinised muscle with the first stimulus, and 

 the return to normal as the stimuli are repeated. The 

 first contraction will probably be higher than the normal 

 one. If the muscle is left unstimulated for about five 

 mins. the prolonged contraction caused by veratrin will 

 again be obtained. 



Instead of this method, a sciatic-gastrocnemius preparation may 

 be left in -001 p.c. veratrin for half an hour, then washed in saline 

 solution, fixed in the muscle chamber and the nerve stimulated. 



Or, 3 or 4 drops of a 1 p.c. solution of veratrin may be injected 

 into the dorsal lymph sac of a brainless frog; and the sartorius or 

 the sciatic-gastrocnemius preparation made when the reflex con- 

 traction is prolonged on pinching the foot. 



4. Effect of cold and heat. Fix the nerve-muscle 

 preparation (1, c) in the muscle chamber. Take a 

 tracing of a single muscle contraction showing the la- 

 tent period, and take the temperature of the fluid with 

 a thermometer. 



Move the drum half way round, run off the fluid, add 

 saline solution at 2 C., leave it for about 3 minutes, 

 take a tracing of a single muscle contraction, take the 

 temperature of the fluid, note the form of the curve so 

 that at the end of the experiment the temperature may 

 be written against it. 



Repeat with saline solution at 20 C. and at 30 C. 



Write on the tracing the temperature at which each 

 curve was taken. Note the differences in duration of 

 contraction. Cold retards the changes in the muscle so 

 that both contraction and relaxation are slowed. The 

 height of the curve depends in part on the upthrow of 

 the lever, and other methods are required to determine 

 the effect of temperature on the degree of contraction. 



