SOURCE OF ANIMAL HEAT. 31 



magnetic disturbances in the animal body can have on 

 the functions of its organs, still the ultimate cause of 

 all these forces is a change of condition in material 

 particles, which may be expressed by the conversion, 

 within a certain time, of the elements of the food into 

 oxidized products. Such of these elements as do not 

 undergo this process of slow combustion, are given off 

 unburned or incombustible in the excrements. 



Now, it is absolutely impossible that a given amount 

 of carbon or hydrogen, whatever different forms they 

 may assume in the progress of the combustion, can 

 produce more heat than if directly burned in atmos- 

 pheric air or in oxygen gas. 



When we kindle a fire under a steam-engine, and 

 employ the power obtained to produce heat by friction, 

 it is impossible that the heat thus obtained can ever 

 be greater than that which was required to heat the 

 boiler ; and if we use the galvanic current to produce 

 heat, the amount of heat obtained is never, in any cir- 

 cumstances, greater than we might have by the combus- 

 tion of the zinc which has been dissolved in the acid. 



The contraction of muscles produces heat ; but the 

 force necessary for the contraction has manifested itself 

 through the organs of motion, in which it has been ex- 

 cited by chemical changes. The ultimate cause of 

 the heat produced is, therefore, to be found in these 

 chemical changes. 



By dissolving a metal in an acid, we produce an 

 electrical current ; this current, if passed through a 

 wire, converts the wire into a magnet, by means of 



