OTHER SOURCES OF ANIMAL HEAT. 347 



ably. Hence it is a purely scientific fact, that 

 the poor and ill-clad creatures who tread our 

 streets, suffer most severely from the calls of 

 hunger, although the sensation may be, per- 

 haps, blunted in many instances by the fre- 

 quency of its exercise. In the case of the poor 

 man, respiration, supplied with but scanty fuel, 

 and called upon to do more than ordinary duty 

 to keep an ill-covered body warm, draws its 

 supply from the structures of the body, and is 

 no doubt the primary cause of that large amount 

 of diseases of debility whose victims are almost 

 exclusively to be found among the poor of this 

 world. 



It is ascertained that, in addition to respira- 

 tion as a source of heat, there are several other 

 causes in the living animal body by which the 

 temperature of the whole system is maintained. 

 In digestion, which is in great part a chemical 

 process, a considerable amount of heat is extri- 

 cated. " Every mechanical movement of the 

 body," observes Mr. R. Hunt, " occasions the 

 development of heat; every exertion of the 

 muscles produces sensible warmth; and indeed 

 it can be shown by experiment that every ex- 

 pansion of muscular fibre is attended with the 

 escape of caloric, and its contraction with the 

 absorption of it. There is no operation of the 

 mind not even the most idle thought which 

 does not excite the latent caloric of the body ; 



