496 Dynamic Theory. 



sible heat. It is abundantly obvious in this case that the galvanic bat- 

 tery which furnishes the irritations, is a substitute for the central 

 ganglions of the nervous system ; viz. , the spinal cord and brain. In 

 life the striated muscle contracts only when stimulated from these cen- 

 ters, and the nature of the stimulation is by these experiments clearly 

 indicated. When a tetanus or continuous contraction of the muscle oc- 

 curs, it is the result of a continuous series of rythmically interrupted 

 pulsations of the nervous current. The experiments show that a single 

 pulsation of the current results in a single contraction of the muscle, fol- 

 lowed by its relaxation ; while, if the current is continuous and uninter- 

 rupted, the contraction takes place suddenly when the current first begins, 

 which contraction is followed b} r relaxation not quite complete, leaving 

 the muscle in a state of partial contraction which continues while the 

 current passes. 



Accompanying the molecular motion of a tetanized muscle is a mu 

 sical sound. This varies in pitch with the rapidity of the irritations or- 

 pulsations of the muscle, which depends on the rapidity with which the 

 ratchet is turned and the current interrupted. The pitch heard during 

 voluntary contraction of the muscles is C ' or D ' , equal to 32 to 36 vi- 

 brations per second. Helmholtz thinks this is the first harmonic of the 

 real tone, which he supposes to be an octave lower, but which is inaudi- 

 ble to the human ear. When the motor nerve trunk, or spinal cord, of 

 an animal is irritated by chemical means, the muscle sound has been 

 found due to 19.5 vibrations. The pitch heard during voluntary con- 

 traction obviously indicates the .number of pulsations or waves of ether 

 per second sent from the brain to the muscle. When the muscle is con- 

 tracted by the artificial irritations of an interrupted galvanic current, the 

 sound corresponds to the pitch due to the number of interruptions per 

 second, and may be made to run up as high as 800 to 1,000. The re- 

 sult is the same whether the irritation is applied to the muscle direct or 

 to its nerve, except that in the latter case the sound is not so loud. 

 The sound is due to rapid molecular changes taking place in the mole- 

 cules of the muscle changes in the density of the muscle, according to 

 Landois and Stirling. 



When the muscle is caused to contract by an irritation delivered from 

 a nerve, it is apparent that the force of the muscle contraction is very 

 much greater than that Of the nerve current which starts it. It must 

 be, then, that the nervous force, when it irritates a muscle, unlocks and 

 liberates an energy much greater than its own. The energy of the 

 bod} 7 , like that of a steam engine, is derived chief!} 7 from the combus- 

 tion of carbon. This combustion takes place in all parts of the body, 

 and it consists, as before stated, in the union of oxygen with the differ- 

 ent tissues of the body, especially the muscles aiid nerves. The oxy- 



