EXTERNAL ORIGIN OF FORCE. 67 



to decry its value in any way, there were, on the other hand 

 some great truths which could only be appreciated by comparing 

 the most highly specialised forms of life with one another, not 

 in their minute details, but in their broad general features. I 

 also observed, that while the chief eosmical function of highly- 

 developed vegetable life was deoxidation, or the separation of 

 oxygen from carbon and hydrogen, the leading function of highly 

 developed animal life was oxidation the recombination of the 

 separated oxygen and carbo-hydrogen with one another ; and 

 we agreed to consider upon this occasion the essential nature of 

 these two correlative processes. I said, further, that I was in- 

 duced to bring this subject under your notice in a more ele- 

 mentary and detailed manner than I originally contemplated, 

 from finding that certain principles believed by physicists to be 

 as fundamental as the laws of gravitation were not heartily and 

 unreservedly admitted by physicians. 



(69.) First of all, then, we have to inquire into the character 

 and import of that deoxidation of carbonic anhydride and water, 

 which takes place in vegetable organisms, and the origin of the 

 forces by which it is brought about. Now, in entering upon the 

 discussion of this question, I must direct your attention for a 

 short time to topics which at first sight seem but very remotely 

 connected either with chemistry or physiology. To paraphrase 

 in sober earnest the expressions used in sarcasm by a very dis- 

 tinguished Fellow of this College, the value of whose contribu- 

 tions to physiological science no one can be more ready than 

 myself to acknowledge, I shall preface my remarks by a few ob- 

 servations upon force and the constancy of its amount in the 

 universe. Then, by a reference to systems and suns, and worlds, 

 and steam-engines, and mills, and telegraphs, I shall endeavour 

 to satisfy you that the same forces are at work in living plants 

 and animals as in the inorganic world ; and that the study of the 

 indestructibility and correlation of force will teach us much, 

 though far indeed from all, concerning the nature of life. 



(70.) Let us begin, then, by considering the correlation that 

 exists between the forces of heat and motion their equivalency 



p2 



