Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
the nerve between the electrodes and the muscle hang down 
in a loop. 
Let the extreme end of the loop dip into a drop of concentrated 
solution of common salt. As soon as the irregular tetanic con¬ 
tractions resulting from the action of saline fluid on the nerve make 
their appearance, pass an ascending current through the electrodes. 
The tetanic spasms will be much lessened or cease altogether. 
Pass a descending current through the electrodes ; the spasms 
will be increased. 
The general irritability, therefore, of the nerve is affected in elec¬ 
trotonus not simply its susceptibility to electrical modifications. 
Obs. X. By introducing a rheochord between the battery and the 
polarizing electrodes and by varying the number of cells used, 
the student will ascertain that the amount of increase of irritability 
in katelectrotonus and decrease in anelectrotonus depends on the 
strength of the polarizing current, being greater with the 
Obs. XI. By placing the polarizing electrodes at a variable dis¬ 
tance from each other, it will be found that, with the same strength 
of current, the effect is greater the longer the piece of nerve 
between the polarizing electrodes. 
Obs. XII. By shifting the exciting electrodes nearer to and farther 
from the polarizing electrodes, it will be found that the effects 
of both anelectrotonus and katelectrotonus are greatest in the 
immediate neighbourhood of the polarizing pair, and diminish the 
farther the exciting pair is from the polarizing. 
In all the above observations, the stimulus, whether electric or 
chemical or other, is brought to bear on the nerve between the 
polarizing pair and the muscle. 
Obs. XIII. They may be repeated with the polarizing pair 
placed between the exciting pair (or chemical stimulus) and the 
muscle. An ascending current will now throw the region of the 
exciting pair into katelectrotonus, a descending into anelectro¬ 
The general results will be the same, but they will not come 
out with the same distinctness, for the following reason. When 
the exciting pair is placed nearer to the muscle than the polarizing 
pair, the nerve between the exciting pair and the muscle is simply 
in a state of katelectrotonus, the intensity of which diminishes 
towards the muscle onwards. There is nothing between the 
exciting electrodes and the muscle to modify the increase of im¬ 
pulse due to katelectrotonus. When the exciting pair is on the 
other side of the polarizing pair, and the region of the exciting 
pair thrown into katelectrotonus, for instance, the increased im¬ 
pulse due to katelectrotonus after passing through the region 
of katelectrotonus, has to make its way through a region 
c c 


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