22 EXPERIMENTAL PHYSIOLOGY. 



large scale pan is attached. Obtain a record of the comparative 

 length of the muscle without weight and with weights increasing 

 by 10 gms. at each trial. The drum should be moved by hand 

 between each increment. Continue until the point of rupture 

 is reached. Plot a curve of these results. 



In a second preparation, add 10 gm. increments, but stop 

 before the muscle is injured. Now remove 10 gms. at a time, 

 securing a record in each case. Plot a curve of the recovery. 

 ^^ In a similar manner obtain records from a rubber band, 

 both for extension and recovery. 



Study the extensibility of a contracted muscle as compared 

 to the same muscle at rest. Arrange a muscle preparation as 

 //^. before. Obtain short records of the muscle at rest and when 

 stimulated by a single maximal break shock without any weight. 

 Continue to do this for 10 gram increments as far as possible. 

 What happens when a load is reached which the muscle cannot lift? 

 rest and when stimulated by a single maximal break shock 

 without any weight. Continue to do this for 10 gram incre- 

 ments as far as possible. What happens when a load is reached 

 which the muscle cannot lift? 



Plot extension curves of the contracted muscle and the 

 resting muscle so that they may be easily compared. 



THE SIMPLE CONTRACTION. 



Although muscle seldom responds by a simple twitch when 

 called into action in the body, its behaviour can be conveniently 

 studied when it gives such twitches. Simple contractions can be 

 caused by single electrical stimuli. In order to observe the action 

 of a single muscle it is isolated from its neighbours and arranged as 

 described in the experimental work so that when contracting a 

 record is made upon the surface of a rapidly rotated cylinder 

 (Fig. 5). By means of a signal magnet and a tuning fork the time 

 required, for the initiation and completion of the action, can be 

 determined. The time elapsing between the application of the 

 stimulus and the first visible contraction is about 0.01 sec. for a 

 frog's gastrocnemius. With the more quickly responding mirror 

 method it is 0.0065 sec. The time consumed in the contraction 



