STRETCH AND MUSCRE RESPONSE 
177 
tically the same, but are followed by a gradual decrease in height 
with the onset and progression of fatigue, and a slow relaxation 
or decrease of tone. Series 13, 14, 15 and 16 were made in 
the same way as the above, with the exception that immediately 
after mounting in the sodium chloride solution, each was stretched 
with a ten gram weight. The length of time of stretch was the 
only varying factor and was for ten minutes, twenty minutes, 
one hour and three hours, respectively. Figure 13 shows very 
little variation from the standard sodium chloride series. The 
relaxation phase is not so evident, but the evidence of fatigue is 
more pronounced. After a stretch of twenty minutes as shown 
in figure 14, the heights of the contractions are much greater and 
also the tonus holds up much better than in the preceding series 
of this group. This suggests, when compared with 12 and 13, 
that stretching sensitizes the muscle to greater contractions and 
enables it to better withstand the onset and progressive effects 
of fatigue. Figure 15, made after stretching one hour, shows a 
marked increase in the height of contraction, but fatigue begins 
at about the same relative time and progresses at about the same 
rate, and the tonus remains practically constant, all of which are 
important when correlated with the previous series. After three 
hours stretching with a ten gram weight a series is obtained as 
shown in figure 16. The height of contraction is not so great, 
the progressive effects of fatigue are more pronounced, and the 
loss of tone is again observed, all of which indicate that the 
point of maximum sensitization has been passed. 
Series 17 to 21 inclusive show the effects of stretching muscles 
in normal potassium chloride solution, with the same weights and 
the same lengths of time, as those in series 12 to 16 respectively. 
Each series of the potassium chloride group possesses the char- 
acteristic initial contraction, followed by a series of curves indi- 
cating marked inhibition as compared with the corresponding 
sodium chloride series. Figure 17 shows the typical or standard 
series of curves when the muscle was not submitted to previous 
stretching. The heights of contractions, following correspond- 
ing stimuli and the resistance to the progressive effects of fatigue 
are much less where potassium chloride is used. In figure 18, 
where stretching continued for ten minutes, the relaxation fol- 
lowing each contraction is much inhibited and the increase in 
tonus continues during several stimuli, followed by a gradual 
loss of tonus and sensitization, reaching complete exhaustion near 
the end. When compared with figure 17 where no* stretching 
