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IOWA ACADEMY OF SCIENCE Vor. XXIX, 19 22 
traction in 5. It is thus evident that the amount of work done 
in lifting the weight is equivalent to that done in the correspond- 
ing contractions where the weight was removed. Apparently there 
was a certain definite amount of sensitizing material present be- 
fore each of the initial contractions following the two hour stretch 
period, and the additional stretch due to lifting the weight lib- 
erated no appreciable additional amount. Figures 10 and 11 
are continuations of series 7 and 9, respectively. In the former 
the muscle is only partly fatigued while in the latter the fatigue 
is practically complete. The sodium chloride solution was re- 
moved in each case and 0.18 per cent amyl alcohol was added, 
and the subsequent curves show the progressive effects of the 
alcohol. While these curves are not exactly comparable due to 
variation in the time between the introduction of the alcohol and 
the application of the stimulus it is quite evident from these and 
other experiments that the increase in sensitization by amyl al- 
cohol in this concentration is most rapidly brought about in 
partly fatigued muscles. 
Series 12 to 31 inclusive are records made to test the effects 
on the normal responses of muscles immersed, stretched and 
stimulated in normal sodium chloride, potassium chloride, and 
calcium chloride solutions. The method used in mounting and 
stimulating the various tissues is the same, but the length of 
time of stretch varies in the different series from ten minutes to 
three hours. The muscles are automatically stimulated with an 
eight volt tetanizing electric current, set to make thirty-eight to 
forty double vibrations each second, with intervals of twenty 
seconds. Each series is selected as typical among many made 
under the same conditions. In each solution used the most marked 
initial sensitization appears in tissue stretched with a ten gram 
weight for about one hour. Sodium chloride produced marked 
sensitization during the longer periods of stretch. Potassium 
chloride produces marked inhibition when compared with sodium, 
while calcium chloride brings about contracture which merges 
into rigor and these factors .hasten proportionately comparative 
fatigue processes. Figure 12 is a record of a muscle when stimu- 
lated immediately after mounting and immersed in normal sodium 
chloride solution, without being stretched, and is a normal or 
standard series under these conditions. It is the same type of 
series as that shown in figure 1 where only six volts were used 
at intervals of one minute, and shows the same, in that con- 
tractions following the first ten dr twelve stimuli remain prac- 
