52 TETANIC CONTRACTIONS. [BOOK i. 



c. On the contrary, it passes from b to /, and so down the pillar d, in the direction 

 indicated by the thin interrupted line, and out to the battery by the wire y. Thus 

 the current is 'short- circuited' from the primary coil; and the instant that the 

 current is thus cut off from the primary coil, an induced (breaking) current is for the 

 moment developed in the secondary coil. But the current is cut off not only from 

 the primary coil, but also from the spirals m ; in consequence their cores cease to be 

 magnetised, the bar e ceases to be attracted by them, and the spring ft, by virtue of 

 its elasticity, resumes its former position in contact with the screw c. This return 

 of the spring however re-establishes the current in the primary coil and in the 

 spirals, and the spring is drawn down, to be released once more in the same manner 

 as before. Thus as long as the current is passing along x, the contact of 6 is 

 constantly alternating between c and/, and the current is constantly passing into 

 and being shut off from p, the periods of alternation being determined by the periods 

 of vibration of the spring 6. With each passage of the current into, or withdrawal 

 from the primary coil, an induced (making and, respectively, breaking) shock is de- 

 veloped in a secondary coil. 



When it has once been realized that an ordinary tetanic 

 muscular movement is essentially a vibratory movement, that 

 the apparently rigid and firm muscular mass is really the subject 

 of a whole series of vibrations, a series namely of simple spasms, it 

 will be readily understood why a tetanized muscle, like all other 

 vibrating bodies, gives out a sound. That a contracting (tetanized) 

 muscle does give out a sound, the so-called muscular sound, is 

 easily proved by listening with a stethoscope to a contracted 

 biceps, or by stopping the ears and listening to the contractions 

 of one's own masseter and temporal muscles. 



When a muscle is thrown into tetanus by interrupted shocks 

 applied directly to the nerve or to the muscle, the note is the same 

 as that of the interruptor determining the number of the shocks. 

 This is naturally the case, since the note of the muscle-sound is 

 determined by the rapidity of the spasms or vibrations which go to 

 make up the tetanus, and these are determined by the rapidity 

 with which the stimulus is repeated. 



When a muscle is thrown into tetanus by the will or by reflex 

 action or by direct stimulation of the spinal cord, in fact, in any 

 way through the action of the central nervous system, the same 

 note is always heard, viz. one of 36 to 40 vibrations per second, 

 which however is probably a harmonic of a lower note indicating 

 that the muscle is really vibrating 19 or 20 times a second. 



It need hardly be said that a single muscular contraction, a 

 single vibration, cannot cause a muscular sound. 



The general observations which have been described in this 

 section may, when proper precautions are taken, be carried out on 

 a muscle-nerve preparation from a frog for a very considerable 

 time after its removal from the body. After some hours however, 

 or it may be days, the length of time varying according to 

 circumstances, it will be found that no stimulus, however powerful, 

 will cause any contraction, when applied either to the nerve or to 

 the muscle. Both muscle and nerve are then said to have lost 

 their irritability ; and a short time afterwards the muscle may be 

 observed to pass into a peculiar condition known as rigor mortis, 



