APPENDIX II. 177 



P 



natters, on the other hand, leave the body with a 

 portion (amount in urea one-seventh) of their poten- 

 tial energy unexpended. 



7. The transformation of potential energy into 

 muscular power is necessarily accompanied by the 

 production of heat within the body, even when the 

 muscular power is exerted externally. This is, 

 doubtless, the chief and, probably, the only source 

 of animal heat. 



