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Observations on the Principle of Vital Affinity, as illustrated by 

 recent discoveries in Organic Chemistry. By WiLLIAM 

 PuLTENEY Alison, M.D., F.R.S.E., Professor of the Prac- 

 tice of Medicine in the University of Edinburgh.* 



PART I. 



The most important steps in a science are those which 

 lead most directly to the establishment of principles or laws 

 peculiar to that science itself, and which constitute its claim 

 to be regarded as a distinct branch of human knowledge. It 

 has been long acknowledged that such is the character of 

 many of those phenomena of living bodies which depend on 

 mechanical movements, or changes of position in their par- 

 ticles, and therefore that the laws of vital contractions are to 

 be regarded as equally elementary and distinctive principles 

 in physiology, as the laws of motion or of gravitation in na- 

 tural philosophy. But a difficulty has been long felt, as to 

 whether a similar claim to peculiarity of the principle on 

 which they depend, can be urged for the chemical phenomena 

 of living bodies. 



In laying down the first principles of Physiology and of 

 Pathology, I have, however, uniformly maintained the exist- 

 ence of a power peculiar to living bodies, and to which the 

 term Vital Affinity, as recommended by several authors, may 

 be properly applied ; — a power by which " the elements of 

 nutritious matter are thrown into the combinations necessary 

 for forming the organic compounds, and restrained from en- 

 tering into other combinations, to which they are prone as 

 soon as life is extinct ; — a power which supersedes and coun- 

 teracts ordinary chemical affinities in living bodies, as com- 

 pletely as vital contractions counteract gravitation or the in- 

 ertia of matter." — (Outlines of Human Physiology, p. 22.) And 

 in delivering lectures on physiology, I always expressed my 



* From " Transactions of the Royal Society of Edinburgh," nearly through 

 the Press. 



