272 Dr Alison on the Principle of Vital Affinity. 



There may be instances of this mode of formation ; but that 

 it should be the usual mode is irreconcilable with the many 

 facts stated. The form and condition of quartz or chalcedony 

 in geodes, as well as the vast amount of this mineral in some 

 cases, —the relative positions of the zeolites, and their occur- 

 rence as incrustations on rocks, or as fillings of cavities or 

 seams, and never in disseminated crystals through the texture 

 of the rock, — ^the green coating of the nodules, which is some- 

 times a carbonate of copper, when there is a native copper in 

 the rock to undergo alteration, — the correspondence between 

 the elements of the minerals and the composition of the in- 

 cluding rock, and at the same time their contrast in being hy- 

 drous, while the constituents of the latter are anhydrous, — 

 and the known formation of zeolites in caverns, — these various 

 facts appear to establish infiltration as the principal means 

 by which amygdaloidal minerals have been produced. 



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. 



(Concluded from p. 146.) 



We may consider, then, the selection and extraction, from 

 a previously existing compound fluid, by the agency of a pre- 

 viously existing compound solid, of certain portions of that 

 fluid already elaborated, as a chemical action, essential to all 

 living beings, and so peculiar to them that it may be, at least 

 with high probability, termed an exercise of a vital affinity. 

 And, in regard to this simplest kind of such action, the fol- 

 lowing points may be considered as ascertained : — 



1. It seems to be always performed, in the perfect vege- 

 table or animal, by an agency, not of vessels, as was formerly 

 supposed, capable of a vital contraction, and of changing the 

 nature of their contents by the degrees of that contraction, 

 but of cells^ either pre-existing in the solid structure, or car- 

 ried about in the nourishing fluid, and having the name of the 



