THE PRINCIPLE OF VITAL AFFIMTY. J 75 



of almost all vegetables,- — that earth existing in large quantity in all fertile soils, 

 whereas it is " very rarely found in the ashes of plants." 



In the animal kindom the same power of simple selection and extraction is 

 more fully exemplified, perhaps most strikingl}^ in the development of many of 

 the lower classes, of Avhich the organization is simple, and the matters deposited 

 from the nourishing fluid remarkably diversified, as in many of the radiata and 

 moUusca, which have horny and earthy integuments. And in all animals, so far 

 as any chemical change is effected in the vital actions of absorption, secretion, 

 and even nutrition, it would appear to be chiefly of this simple kind, consist- 

 ing in the selection and appropriation of compounds already existing in the 

 fluids on which these functions are performed, not in the formation of new 

 compounds. The chyme which is found in the intestines of an animal during 

 digestion contains all the compounds (albuminous, fatty, and extractive matters) 

 which are found in the chyle absorbed from it, although these are in a diiferent 

 state of aggregation, and associated also Avith other matters which are not ab- 

 sorbed. Since it has been ascertained that the compounds which used to be 

 thought peculiar to the greatest secretions in the body, the bile and the urine, 

 pre-exist in the blood, and are only evolved at the liver and kidneys, — accumu- 

 lating, therefore, in the blood, when the secretive action of these organs is sus- 

 pended, — it has become obvious that the main office of these organs is not forma- 

 .tive, but only attractive, to extract from the blood compounds already existing 

 there. And, although there is one material extensively employed in the forma- 

 tion of animal textures, viz., gelatin, which cannot be detected in the blood ; yet, 

 as this is the only material so employed which cannot be found there, and as a 

 substance very closely resembling it is found there under certain circumstances, 

 we may assert that in animals by far the gi-eater part of the act of nutrition, 

 numerous and diversified as the compounds forming the solid materials of animal 

 bodies may be, is likewise of this simple kind. 



We may consider, then, the selection and extraction, from a previously exist- 

 ing compound fluid, by the agency of a previously 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 following points may be considered as ascertained : — 



1. It seems to be always performed, in the perfect vegetable 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 carried about in the 

 nourishing fluid, and having the name of the globules or corpuscules of that 

 fluid. Most of the textures seem to be formed by the gradual transforma- 

 tion, elongation, or flattening of cells, which have sprung from nuclei at- 



