300 



PRACTICAL PHYSIOLOGY 



again, and the pins on the frame 

 are slowly brought up against the 

 two keys in turn and the points 

 along the curve marked at which 

 the two stimuli entered the muscle; 

 the second stimulus should have 

 fallen well within the latent period 

 of the first. Reset the apparatus, 

 leaving K 2 horizontal, but placing K } 

 vertical, and record the contraction 

 due to the first stimulus alone. 

 This second contraction will be 

 found to be smaller than that caused 

 by the summation of the two sub- 

 maximal stimuli. 



Fig. 181 shows the contractions 

 obtained by a Pendulum Myograph 

 which is fundamentally the same as 

 a spring myograph, and differs only 

 in that the smoked plate, instead of 

 being shot horizontally across by a 

 spring, swings across at the end of 

 a long and heavy pendulum and 

 describes an arc of a circle. 



The glass plate in either case is 

 varnished in the ordinary way, and, 

 when dry the curves are reproduced 

 by exposing to daylight sensitive 

 paper covered by the smoked plate. 



