180 
IOWA ACADEMY OF SCIENCE Voi.. XXVIII, 1921 
ation of the experiment, a double Deprez signal was used, one 
magnet activated by the primary circuit recording the stimulus 
applied, and the other connected with the Harvard type chro- 
nometer beating half minutes. As a check on the variation in 
temperature throughout the series of experiments, a thermometer 
was mounted within a glass chamber. From extended prelimi- 
nary observations it was found that the optimum strength of cur- 
rent was about six volts (three fully charged storage cells of 
about two volts each). The secondary coil of the inductorium 
was used in its fully closed position in practically all of the experi- 
ments herein described, and as a check on the effect of resistance, 
various lengths of calibrated German silver wire of a Harvard 
long typed rheocord were used. The effect of such resistance 
when thrown into the secondary circuit will be discussed below. 
In certain experiments an automatic circuit breaker was used, 
mounted and mechanically impelled by a Harvard type kymograph 
mechanism.* All records were obtained upon a slowly revolving 
kymograph (one revolution in sixty minutes) so that from this 
factor they are comparable. The factor of sluggishness in res-, 
ponses in most muscles used made it necessary to use for the 
most part the tetanizing current, and for this the inductorium was 
set as an interrupter, the number or rate of the stimuli being 
automatically regulated by the contact device on the kymograph 
just referred to. In most of the experiments, not less than thirty-- 
six nor more than forty double stimuli were employed, any excep- 
tions to this rate being stipulated on the records in each case. 
Different muscles of various animals were used in the course of 
the experiments ; i.e., tissue of the regions of the esophagus, 
stomach, intestine and oviduct of the frog ; regions of the esopha- 
gus and stomach of the turtle; the circular muscles of the body 
wall and the intestinal tract of the earthworm in certain regions 
fulcrum of the lever was mounted in a way that by turning a fine threaded screw, ad- 
justments could be made for the point to compensate for “stretch” of the muscle or 
other necessities, and could if desired be maintained at a level of a “base-line.” Ad- 
justment could be made easily and quickly without interfering with other manipula- 
tions. The glass chamber was provided with a stoppered outlet at its base so that 
fluids could be drained quickly by pressing a stop-cock. A funnel mounted just above 
the mouth of the tube facilitated pourjng the liquids in, and was so inclined that fluids 
poured would strike the sides of the tube without “splash,” and would gradually sub- 
merge the muscle. In each case after alcohol was used the funnel and glass chamber 
were rinsed out with distilled water. 
* This modification consisted chiefly of mounting securely the binding posts of a 
Zimmerman contact breaker upon the top plate of the kymograph, and mounting a 
circular-like breaker tract of heavy copper wire upon the revolving spindle. By trials, 
the time of contact could be determined and accurately calibrated against a standard 
chronometer. 
