486 STUDIES IN GENERAL PHYSIOLOGY 
preparations. When a spark passes there is nothing to 
keep the electricities in the muscle preparation apart, and a 
current consequently passes longitudinally through the 
nerves and causes the muscles to contract. 
b) The muscle preparations lie at a right angle to the path . 
of the spark, but in a position symmetrical with reference to 
the spheres of the discharger (Fig. 140). The electricities 
will now be distributed in the preparation in such a way 
that during the passage of the spark a current must pass 
es a 
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FIG. 141 
transversely through the nerve. Since the nerve cannot be 
stimulated by a current passing transversely through it, the 
effect is in this case minimal. 
c) The nerve-muscle preparations again lie parallel with 
the spark discharge, but not in a position symmetrical with 
reference to it, but toward one side of it (Fig. 139). The 
electricities will now be so distributed that during the dis- 
charge a current must pass transversely through the nerve. 
We must therefore again expect a minimal effect, etc. 
The experiment with a mirror which I described in a 
previous paper, and which at first seemed to contradict our 
explanation, can also be explained in this way. The nerve- 
muscle preparations were placed at right angles with the 
spark discharge, but not in a position symmetrical with the 
discharger, but slightly to one side of it (Fig. 142). Under 
such circumstances only a weak current passes longitudi- 
nally through the nerves during the passage of the spark. 
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