SECT. i. ELECTRIC CURRENTS IN THE MUSCLES. 7 



now in one direction and now in the other, according 

 as he contracts his right arm or his left. The electri- 

 city thus evolved, when conveyed to the needle through 

 several miles' length of coiled insulated wire, will cause 

 a deflection amounting to sixty or seventy degrees, ac- 

 cording to the strength of the man that is, according 

 to his muscular and nervous force ; the amount of the 

 electricity being exactly in proportion to the amount 

 of muscular force. 



It appears that the electric currents in the nerves are 

 eight or ten times stronger than those in the muscles. 

 M. Helmholtz found that the time required to contract 

 a muscle, together with the time required to rela,x it 

 again, is not more than the third of a second, and is a 

 constant quantity, for the compensation of energy pre- 

 vails also in organic nature. He also found that the 

 motion or velocity of the electric current in a man is 

 at the rate of 200 feet in a second. The electric equi- 

 valent, as determined by M. Helmholtz, is equal to the 

 electricity produced in a voltaic battery by the seven 

 millionth part of a milligramme of zinc consumed in the 

 ten-thousandth part of a second, a milligramme being 

 the 0'015432 part of a grain. 



The contraction and muscular action or mechanical 

 labour produced by the passage of an electric current 

 through a nerve is 27,000 times greater than the me- 

 chanical labour which results from the heat disengaged 

 by the oxidation of that small quantity of zinc requisite 

 to generate the electricity ; that is to say, the mecha- 

 nical labour really produced by the contraction of the 

 muscles is enormously greater than the labour corre- 

 sponding to the zinc oxidized. In fact, the electric ex- 

 citement of a nerve is analogous to an incandescent 

 particle or electric spark that sets fire to a great mass 

 of gunpowder. This result, and the association between 

 the greatest activity of respiration and the intensity of 



