488 APPENDIX 



Hold key No. 1 closed. Without making a curve (using the myograph 

 merely to see better the contraction), close key No. 2 and hold it closed, 

 whereupon the make-current from the second cell will stimulate the 

 muscle. Now, with this current still passing through the muscle, open 

 key No. 1, which lets the current from cell No. 1 into the circuit and 

 doubles the intensity of the stimulus. The muscle then contracts again. 



(B) Gradual Change. Hitch the two dry-cells in series, and interpose 

 between them and the myograph a simple key and the rheocord. Place 

 the block of the rheocord against the anodal binding-post and close the 

 key. Now slide the block along the meter of wire visible on the rheocord 

 to its end and observe that no contraction occurs although the stimulus 

 has risen from below the threshold to far above it. Raise the block off 

 the wire and replace : there is active contraction from this sudden stimu- 

 lation although no stronger than before. 



Expt. 45. Summation of Singly Inadequate Stimuli. (Apparatus: 

 Inductorium, frog). (A) In Reflexions. Tie the wires from the secondary 

 coil about a frog's foot not too close together. Stimulate with make- 

 shocks below the threshold for reflex contraction of the leg. Soon the 



FIG. 272 



Summation of singly inadequate stimuli, to show a probable katabolic influence on protoplasm. 

 At intervals of three seconds a frog's gastrocnemius was stimulated with break-shocks, each too 

 weak to produce a contraction. After about sixty such stimulations contraction occurred. (To 

 be read from left to right.) The time-line is in three-second intervals. This result, made on 

 a "winter-frog," is not like that seen in the "summer-frog." 



influences summate and the leg is flexed. (B) In a Single Muscle. Place 

 the secondary coil so that the single break-shock is just below the thres- 

 hold-intensity. After the muscle has fully recovered from the stimulation 

 of this threshold-finding, let a break-shock pass through the muscle 

 (always excluding makes) and repeat at intervals of four or five seconds 

 by the watch. These stimuli after a time will summate to an effective 

 stimulus, and the muscle will contract. 



This experiment studies the summation of the occasion of contraction 

 just as the next experiment deals with the effect. It demonstrates that 

 even a subliminal stimulus (one below the threshold-strength) has an 

 effect on protoplasm which persists in some form at least five seconds 

 (in fact, twice that time at least). We see this frequently in the sensory 

 realm also. (See Chapter XII.) The precise nature of the impression 

 made on protoplasm by subliminal stimuli cannot be stated, but it lies 

 probably in the direction of increasing slightly each time the tonus or 

 irritability of the tissue. 



Expt. 46. Superposition of Contractions. (Apparatus : Myograph and 

 indue torium.) Arrange apparatus for writing myograms through 

 single maximal shocks, the drum rotating at its maximum gear-speed. 



