STRETCH AND MUSCLE RESPONSE 
179 
the earlier periods of stretch than in the corresponding potassium 
series, while in those of the longer periods of stretch the reverse 
is true. Also following the initial contraction the tonus is in- 
creased during several stimuli and maintained in a comparatively 
striking manner throughout each series of the calcium group. 
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SUMMARY 
Mounts of intestine and body wall muscles of the earthworm 
when immersed in normal sodium chloride solution and stretched 
for various intervals with ten gram weights and subsequently 
uniformly but intermittently stimulated with a tetanizing current 
of known strength at successive intervals, (i. e. each minute for 
one-half hour) show that stretching has a sensitizing effect in 
the responses immediately following the treatment which is rela- 
tively proportional to the duration of the stretch up to certain 
limits. Noticeable relationships are found between duration of 
stretch and the onset of fatigue which in general seem to indi- 
cate that the greater the stretch, the greater the initial sensitiza- 
tion followed by rapid onset of fatigue. 
Mounts stretched with different weights in normal sodium 
chloride, potassium chloride and calcium chloride solutions and 
stimulated every twenty seconds for a period of fifteen minutes 
show remarkable correlation between duration of stretch, in- 
tensity of stretch and the kinds of solutions used together with 
characteristic comparative differences in the types of curves pro- 
duced. In all solutions the most marked initial sensitization ap- 
pears in tissue stretched by ten gram weight for about one hour 
duration. Potassium chloride produces marked inhibition when 
compared with sodium, while calcium chloride brings about con- 
tracture which eventually merges into rigor and these factors 
hasten proportionately comparative fatigue processes. 
These results help to substantiate a belief that stretching a 
muscle involves the liberation of certain amounts of energy which 
in turn call forth certain metabolic changes. These changes ap- 
parently produce stimulating substances, which on further trans- 
formation, by stretching yield toxic properties. Further, these 
inner changes can be markedly modified by environmental condi- 
tions, a point of wide significance in making physiological in- 
terpretations. 
EXPLANATION OF FIGURES 
The series of curves in each of these figures was selected 
after eight to twenty-five had been made under exactly the same 
