Dr Alison on the Principle of Fital Affinity. 135 



mitted, that there are Attractions and Repulsions, as well as 

 contractions, peculiar to the living state : chiefly, but not ex- 

 clusively, observed at those parts where chemical changes are 

 effected in living bodies, and connected with these changes ; 

 and, without reference to this general fact, I maintain that it 

 is impossible to have a right understanding of many pheno- 

 mena of essential importance in physiology and pathology.* 



But the general principle is obviously equally applicable 

 to chemical changes as to mechanical movements. It is not, 

 indeed, so easy to ascertain, in regard to chemical changes 

 in living bodies, that they are truly inconsistent with the che- 

 mistry of dead matter ; the science must be allowed to make 

 some progress before this can be confidently asserted in re- 

 gard to any individual chemical change ; but no one can doubt 

 that, as science advances, it must become possible to say with 

 certainty, whether the chemical changes in living bodies are 

 consistent with those laws which regulate chemical changes 

 elsewhere, or not ; i. e., whether the same chemical elements 

 can be so brought together by the chemist, as to tend to the 

 same combinations as are found in living bodies ; or whether, 

 in his hands, they will enter uniformly into other combina- 

 tions, and form different compounds. 



Farther, it appears to me that, even before any of the re- 

 cent discoveries, it might be legitimately inferred from facts 

 already known, that this last description is truly applicable, 

 in some cases, to the chemistry of living bodies. It was 

 knowU; for example, that when water, impregnated with car- 

 bonic acid and with a small proportion of ammonia, is brought 

 into contact with vegetable substances, in a certain stage of 

 their existence, the elements of these bodies rapidly combine 

 so as to form starch, albumen, and oil, which are added to 



* Professor Whewell, in his instructive abstract of the general principles 

 ascertained in Physiology, regards it as established, chiefly on the authority of 

 Mulder, in regard to the vital force concerned in assimilation and secretion, that 

 •' it has mechanical efficacy, producing motions, &c. But it exerts at the same 

 point both an attraction and a repulsion, attracting matter on one side and re- 

 pelling it on the other ; and in this it diffei-s entirely from mechanical forces.' — 

 Philosophy of Inductive Sciences, vol. ii., p. 51. 5See also Carpenter's Manual of 

 Phyriology, § 697, et seq. 



