552 PHYSIOLOGY. 



The Effects of Two Successive Stimuli. Let the student imagine 

 two successive momentary stimuli applied successively to a muscle. 

 The stimuli may be either maximal or submaximal; that is, either 

 the greatest possible contraction the muscle is able to accomplish or 

 only a medium contraction from the applied stimulus. 



Fig. 197. Rate of Conduction of the Contraction Process along a 

 Muscle as shown by the Difference in the time of Thickening of the two 

 Extremities. (MAREY, HOWELL.) 



The tuning-fork waves record Vioo of a second. 



If each of the two stimuli be maximal, the effects produced will 

 vary according to the time of application of the two excitants. Thus, 

 (1) if the second stimulus be applied after the relaxation following 

 the effect of the first stimulus, then the myogram shows two maximal 



Fig. 198. Tracing of a Double Muscle-curve. ( FOSTER.) 



To be read from left to right. 



While the muscle was engaged in the first contraction (whose complete 

 course, had nothing- intervened, is indicated by the dotted line), a second 

 induction shock was thrown in at such time that the second contraction began 

 just as the first was beginning to decline. The second curve is seen to start 

 from the first as does the first from the base line. 



contractions; (2) if the second stimulus follow the first with such 

 rapidity that the two occur during the latent period of the muscle- 

 curve, then the recording instrument shows but one maximal con- 

 traction. 



