1 870.] BARKER — ON VITAL AND PHYSICAL EORCES. 427 



as heat within the body, the actual loss of heat by the j^roduction 

 of motion is the equivalent of the 350 foot-tons which represents 

 external work. This by a simple calculation will be found to be 

 250,000 heat units, almost the precise amount by which the heat 

 yielded by the food when burned without the body, exceeds that 

 actually evolved by the organism. Moreover, while the total 

 heat given oft' by the body is 2,500,000 units, the amount of 

 energy evolved as work is equal to about 600,000 heat units ; 

 hence the amount of work done by a muscle is, as above stated 

 one-fifth of the actual energy derivable from the food. One point 

 further. The law of correlation requires that the heat set free 

 when a muscle in contracting does work, shall be less than when 

 it effects nothing ; this fact, too, has been experimentally estab- 

 lished by Heidenhain.-^ So, again, when muscular contraction 

 does not result in motion, as when one tries to raise a weif>'ht too 

 heavy for him, the energy which would have appeared as work, 

 takes the form of heat : a result deducible by the law of correla- 

 tion from the steam-engine. 



The last of the so-called vital forces which we are to examine, 

 is that produced by the nerves and nervous centers. In the nerve 

 which stimulates a muscle to contract, this force is undeniably 

 motion, since it is propagated along this nerve from one extremity 

 to the other. In common language, too, this idea finds currency 

 in the comparison of this force to electricity ; the gray or cellular 

 matter being the battery, the white or fibrous matter the conduc- 

 tors. That this force is not electricity, however, Du Bois-Rey- 

 mond has demonstrated by showing that its velocity is only 97 feet 

 in a second, a speed equalled by the greyhound and the race-horse.^" 

 In his opinion, the propagation of a nervous impulse is a sort of 

 molecular polarization, like magnetism. But that this aaent is a 

 force as analogous to electricity as is magnetism, is shown not only 

 by the fact that the transmission of electricity along a nerve will 

 cause the contraction of the muscle to which it leads, but also by 

 the more important fact that the contraction of a muscle is excited 

 by diminishing its normal electrical current ; ^^ a result which could 

 take place only with a stimulus closely allied to electricity. Nerve- 

 force, therefore, must be a transmuted potential energy. 



AVhat, now, shall we say of that highest manifestation of animal 

 life, thought-power? lias the upper region called intelligence 

 and reason, any relations to physical force? This realm has not 

 escaped the searching investigation of modern science ; and 



