32 PRACTICAL PHYSIOLOGY 



two or three minutes with a brass block at the tem- 

 perature of ice (or by placing a piece of ice in 

 contact with the muscle). 



Finally take a tuning-fork tracing below the 

 abscissa. 



Notice the effect of heat and cold respectively 

 upon the period of latency and upon the amount 

 and duration of the contraction. 



Effect of fatigue on muscular contraction. 

 The same or a similar nerve-muscle preparation 

 may be used as in the last experiments, but if the 

 same it should be allowed to resume the normal 

 temperature of the room. Make a new abscissa, 

 and mark, as usual, upon it the point of stimula- 

 tion. Take a normal curve. Remove the writing 

 point from the drum, which is allowed to revolve 

 continuously and to stimulate the muscle with each 

 revolution. After about twenty of such excita- 

 tions without record, apply the lever point again 

 to the drum (making use, of course, of the stop), 

 and let the muscle describe another curve at the 

 same place as the first. Remove the writing point 

 again for the duration of about twenty excitations, 

 and repeat the above procedure a number of times 

 until the fatigue curves are very pronounced. 

 Notice the effects of fatigue upon contraction, 

 prolonging the latency period, diminishing the 

 amount and slowing the course of the contraction, 

 and greatly delaying, and at length even prevent- 

 ing, the relaxation of the muscle. 



A fatigue curve or series of curves can also be 

 obtained by recording every contraction that is, by 



