190 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
PEATE V. 
Explanation of Figures 
1, 2. Typical curves ' of the anterior region of the frog stomach 
showing influence of the- duration of stimulus. Tetanizing current of 
two and a half and five seconds respectively was used. Note the rela- 
tive heights, the similarity of plateau, and a slight difference in relaxa» 
tion in the two curves. Note that the latency phase is very marked 
and rather long. 
3. Typical curve of response of the middle region of the frog stomach 
caused by tetanizing current of about two seconds duration. Note ,a 
rapid decline in relaxation which is fairly typical of this region. 
4A, 4B. Two responses of the posterior portion of frog stomach show- 
ing relative differences in position of a secondary contraction induced by 
some unknown cause on the relaxation of the first. A tetanizing current 
of two seconds duration was used entering as indicated by the signal in 
each case. Note the rather long latency in both. 
5. Record of rhythmical contraction of frog stomach, a condition oc- 
casionally met with upon first mounting tissue of this region. This 
rhythm diminishes gradually in height and passes off usually within fifteen 
to twenty minutes. 
6. Two curves produced on the same tissue from the frog esophagus, 
keeping the duration of the tetanizing stimulus constant in each case. 
Note the almost exact duplication of the first A ten minute interval be- 
tween compensated for fatigue factor. These two curves, due to equal 
stimulation, are instructive when compared to 1 and 2 where the duration 
of the stimulus varied. ■ 
■ 7. Response of the duodenal region of the frog intestine when O.S vol. 
per cent ethyl alcohol is added. The first curve was produced by tetan- 
izing curreqt of five seconds duration, the much higher curve resulted 
after entering the alcohol and stimulating for same length of time. 
8. Typical curve showing the occurrence of rhythmical contractions on 
the relaxation phase of frog stomach, after stimulation soon after mount- 
ing. This sort of curve often resulted if the tissue was stimulated before 
the rhythmical contraction ceased. 
9. ‘The gradation in responses in frog esophagus due to different 
amounts of resistance being thrown in by means of a rheocord. Begin- 
ning with the third curve shown note the diminution of height as suc- 
cessively 50 cm,, 1 meter, and 20 meters of resistance wire were thrown in. 
10. 12. Typical curves showing the effect ' of resistance in diminishing 
responses in earthworm muscle. The introduction of 20 meters resistance 
cuts the resulting response to about half of the preceding normal as can 
be seen here. Finally, weak strength of ethyl alcohol was added and a 
response recorded under its influence, with striking results in each case. 
11. Typical curve of response of anterior end of frog esophagus, show- 
ing a slightly different contour from those of stomach mentioned above. 
