CHAPTER XI 

 MUSCLE AND NERVE 



THE phenomena of muscle and nerve can most 'easily be 

 studied in cold-blooded animals. The frog's gastrocnemius 

 serves this purpose well, and when the sciatic nerve supplying 

 it is carefully left attached, there results a nerve-muscle pre- 

 paration. If the nerve of such a preparation is in any manner 

 excited, the muscle responds by a sharp and quick contraction 

 or twitch. The excitation of the nerve has given rise to a 

 disturbance of unknown nature in the substance of the nerve, 

 which passes rapidly along its length to the motor end plate 

 and excites the muscle fiber, which responds by exhibiting its 

 most characteristic function, contraction. 



Any external influence which can excite living matter to 

 action is an irritant or stimulus. There are five classes of 

 stimuli mechanical, thermal, electrical, chemical, and physio- 

 logical. The quantitative effect which these produce upon 

 living matter depends not only upon their efficiency, but also 

 upon the degree of irritability of the living material upon which 

 they act. The most desirable stimulus for experimental pur- 

 poses is the electrical current, which produces very little injury 

 and may be finely graded as to strength, time, and place of 

 application. It may be either a constant or induced current. 

 The former, also called voltaic current, is such as is furnished 

 by any cell like a Grove or Daniell. The latter is obtained 

 by the use of an induction coil. This instrument consists 

 essentially of two coils of copper wire, one of which is placed 

 within the other, but between which there is no metallic connec- 

 tion. The inner coil of heavy wire (primary coil) is connected 

 with a source of electricity, like a cell. The ends of the outer 

 coil (secondary coil), which consists of many turns of fine wire 

 carefully insulated, are connected with electrodes, by means 

 of which the induced current is applied to the tissues to b 

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