131 APPENDIX II. 



cliemical change which food suffers in the body of an 

 animal that liberates the previously pent-up forces 

 of that food, which now make their appearance in 

 the form of actual energy as heat and mechanical 

 motion. 



From food, and food alone, comes the matter of 

 which the animal body is built up ; and from food 

 alone come all the different kinds of physical force 

 which an animal is capable of manifesting. 



The two chief forms of force thus manifested are 

 Heat and Muscular motion or mechanical work, and 

 these have been almost universally traced to two 

 distinct sources the heat to the oxidation of the 

 food, and the mechanical work to the oxidation of the 



This doctrine, first promulgated, the speaker 

 believed, by Liebig, occupies a prominent position 

 in that philosopher's justly celebrated Cliemico- 

 Pliysiological Essays. 



In his work entitled Die organische Chemie in 

 Hirer Anwendung auf Physiologic und Pathologie, 

 Braunschweig, 1842, Liebig says : " All experience 

 teaches that there is only one source of mechanical 

 power in the organism, and this source is the trans- 

 formation of the living parts of the body into life- 

 less compounds. . . . This transformation occurs in 

 consequence of the combination of oxygen with the 

 substance of the living parts of the body." And 

 again, in his Letters on Chemistry, 1851, p. 366, 

 referring to these living parts of the body, he says : 

 " All these organized tissues, all the parts which 

 in any way manifest force in the body are derived 



