THE ANIMAL AS A PRIME MOVER. 331 



voltaic electricity, and thus unquestionably subject to all the laws of 

 energetics, of electro-dynamics, of electrical physics, and of electro- 

 chemical action. 



The velocity of transmission of the nerve impulse is from 90 feet per 

 second in cold-blooded to 100 or 150 feet in warm-blooded creatures — 

 an exceedingly minute fraction of the speed of the electric current 

 over good conductors. It thus requires about the tenth part of a sec- 

 ond to telegraph from the brain to the extremities and obtain a 

 response through the sensory nerves or to produce reflex motions of 

 muscles. Du Bois Keymond found the electro-motive force impelling 

 the electric currents flowing in the nerves and muscles of the frog to 

 have the value of 0.22 to 0.25 volt in the nerve and 0.35 to 0.75 volt in 

 the muscle. 1 Should it prove the fact that the active energy is electric 

 and magnetic, the low voltage, if confirmed by measurement of the actu- 

 ally operating currents doing their regular and normal work, would 

 indicate great strengths of currents at low tensions. The time required 

 for action at the nerve center itself is something like 0.05 second. 



Matteucci found that the passage of the electric current from the 

 brain toward the extremities produced contractions of the muscles 

 traversed, while the opposite direction of current caused annoyance, 

 if not actual pain, and seemed only to affect the sensory nerves. He 

 thought that this " polar condition " indicated that such excitation by 

 something analogous to, if not identical with, the electric form of 

 energy constitutes the " nervous agency" of the system. 



What is known to-day simply shows that electricity of low tension 

 and comparatively large quantity, or some related form of energy, is 

 or may be a product of transformations occurring in the body, having 

 their source in the potential energy of the food supplied, and is the 

 probable intermediary between the directing power of brain and spine 

 and the elements of the voluntary and involuntary systems of muscles; 

 that this energy is probably in constant circulation in continuously 

 acting organs, and intermittently, at least, in those actuated only by 

 the will; and that the evidence of its presence may always be found in 

 its leakage currents. It is certain that the production of electricity 

 may be increased by the special development of its producing organs 

 to such extent as to become a source of power and of safety to its user 

 and of danger to enemies, exhibiting all the characteristic properties 

 of the familiar forms of moderately high-tension currents. 



Anatomists familiar with comparative biology know that the electric 

 cells of the torpedo and its congeners are evolved from the under side 

 of the skin, and by a process which seems simply that of muscle-cell 

 production, with modification to its special purpose. This fact may be 

 accej)ted as evidence, worthy of consideration at least, that the muscles 

 contain within themselves the principle of animal power, and possibly, 

 even, that this power is a modification of, if not identical with, the 



1 Encyclopedia Britaimica. Article "Physiology," page 26. 



