174 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
per second. Forty to forty-five of these make and break shocks 
constituted the stimulus after each time interval through the en- 
tire series of experiments. The solutions in which the muscles 
were immersed were drained off and replaced with fresh solu- 
tion after each series which ran thirty-five minutes or more, and 
after every second or third where each ran fifteen or twenty min- 
utes. In each case where there was a change made in the kind 
of solution used, the glass tube which was to contain the muscle 
was thoroughly rinsed with the solution next to be used. The 
earthworms used in these experiments were Helodrilus caligino- 
sus var. trapezoides (Duges). These were collected in the field, 
placed in jars with moist earth, and kept at room temperature, 
sometimes for several days before being used, with a variation 
of only two or three degrees from 70° F. All the experiments 
were performed at room temperature, the variation of which was 
so slight that the resulting effects on the muscle may be con- 
sidered as being practically negligible. Sections of ten somites 
of the earthworm constituted the unit of muscular tissue used 
in each case and were taken from behind the clitellum as it was 
found that these were more easily standardized. The sections 
were mounted and stimulated as previously described in the paper 
mentioned above. 
Figures 1 to 5 inclusive are records of typical experiments indi- 
cating the effects of variation in length of time of stretch upon 
the responses of the muscle when* immersed in normal sodium 
chloride solution, the time varying from ten minutes to three 
hours. Each muscle was mounted as previously described and 
given thirty-five to forty stimuli with one minute intervals. Fig- 
ure 1 of Plate I shows what may be considered a typical record 
of responses without stretching. The type of the curves is uni- 
form, varying principally in the heights of contraction, indicating 
the gradual onset and progression of fatigue. The relaxation or 
loss of tonus begins with the initial stimulus and continues uni- 
formly to the later part of the series where the sodium chloride 
is removed and .12 per cent amyl alcohol is added which immed- 
iately sensitizes the tissue to a greater height of contraction and 
a rise of tonus. The progressive inhibitive effects of the alcohol 
are shown in the last few curves of the series. In the first few 
curves of each of the series, 2, 3, 4, and 5, the tissue was stimu- 
lated immediately after mounting and before stretching, follow- 
ing this a ten gram weight was added to each for ten minutes, 
twenty minutes, thirty minutes and two hours, respectively. The. 
