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IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
occurred, one also observes the increase in the initial contrac- 
tion. Figures 19 and 20 record the effects of stretch in nor- 
mal potassium chloride for twenty minutes and an hour and fif- 
teen minutes, respectively, and show the same general effects 
as already mentioned but in a more pronounced way. Thus in 
series 18, 19 and 20 there is a progressive increase in the height 
of the initial contraction and also an increase in the duration 
of the maximum contractions following, which is similar to 
series 13, 14 and 15. This is interpreted as indicating that the 
depressing effects produced by the potassium chloride are more 
than counterbalanced by the sensitizing effects produced by 
stretching. Figure 21 records results of stretching for three hours 
and is strikingly similar to figure 18, the principal differences 
being the variation in the heights of the initial contractions and 
the tonicity during the latter parts of the experiments. The point 
of maximum sensitization has evidently been passed and the 
muscle is approaching rigor. This, in a general way, coincides 
with the results recorded in the sodium chloride series. Series 
22 to 26 inclusive were performed to test the effects of variation 
in the amount of weight used, in stretching muscles when they 
were immersed in normal potassium chloride solution. The ex- 
periments were performed as in the previous potassium chloride 
series excepting that a twenty gram weight was used instead of 
ten grams for the same lengths of time as in the series 17 to 21, 
respectively. The maximum sensitization point was reached 
sooner, being most evident after ten to twenty minute stretch 
while in the potassium series where a ten gram weight was used 
this point was reached after about one hour and fifteen minutes 
stretch. The onset of fatigue is sooner and its progressive effects 
are more pronounced where the greater weight is used. Series 
25 and 26 show results after stretching one hour and three hours, 
respectively. There is little response as compared with series 20 
and 21, showing that a condition of practically complete fatigue 
is reached. 
The records in series 27 to 31 inclusive are of muscles stretched 
in normal calcium chloride solutions for periods of time com- 
parable to the sodium chloride series 12 to 16, and the potassium 
chloride series 17 to 21 and show that the initial contractures fol- 
lowing the shorter periods of stretch are greater than in the cor- 
responding series of the other solutions, while for the longer per- 
iods of stretch the reverse is true. The progressive effects of 
fatigue following the initial contractions are less marked during 
