{ 165 ) 



XVII. — Observations on the Principle of Vital Affinity, as illustrated hy recent 

 discoveries in Organic Chemistry. By William Pulteney Alison, M.D., 

 F.R.S.E., Professor of the Practice of Medicine in the University of Edin- 

 burgh. 



(Read, 2d February 1846.) 



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 aclmowledged that such is the character of many of those pheno- 

 mena of living bodies which depend on mechanical movements, or changes of po- 

 sition in their particles, 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 natural philosophy. But a difficulty has 

 been long felt, as to whether a similar claim to peculiai-ity of the principle on 

 which they depend, can be urged for the chemical phenomena of living bodies. 



In la3ang down the first principles of Physiology and of Pathology, I have, 

 however, uniformly maintained the existence 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 necessaiy for forming the organic compounds, and 

 restrained from entering into other combinations, to which they are prone as soon 

 as life is extinct ; — a power which supersedes and counteracts ordinary chemi- 

 cal affinities in living bodies, as completely as vital contractions counteract gra- 

 vitation or the inertia of matter." — {Outlines of Human Physiology, p. 22.) And 

 in delivering lectures on physiology, I always expressed my belief that a time 

 would come, when discoveries in the chemical department of the science, — connect- 

 ing the ingesta of living bodies with the nourishment of their diiferent textures, 

 and with the nature of the dififerent excretions, — would elucidate the chemical 

 changes which are continually going on in them, and are essential to their living 

 state, as completely as the discovery of the circulation of the blood illustrated 

 many of the conditions of the existence of living animals. It appears to me that 

 this anticipation has been more nearly realized by recent chemical observations, 

 than professed physiologists have yet admitted ; — that not only the existence of 

 the principle of vital affinit}^ has been established, but its limits and mode of 



VOL. XVI. PART II. 2 T 



