Dr Alison on the Principle of Vital Affinity. 277 



different fluids, brought in contact with a solid body, are at- 

 tracted into its pores with very different degrees of force.. It 

 is not the nature of the process by which the selection, in the 

 case of the living body, is effected ; but the peculiarities of 

 the selections themselves, their great force, and yet uniformly 

 temporary existence, that entitle us to regard them as indi- 

 cating a vital property. 



II. But when we attend to the peculiar changes effected 

 by living solids on the fluid matters which are brought in con- 

 tact with them, we find that these are by no means confined 

 to the selection and appropriation, at particular points, of com- 

 pounds pre-existing in that fluid ; but that, under the influ- 

 ence of the living solid, /raw^or//2o//(?w5 or new arrangements 

 of the chemical elements take place, and new compounds are 

 formed. 



In regard to tlie precise nature, or seat, of some of these 

 transformations, there is considerable difficulty, but we are 

 at present concerned only with the principle ; and may state 

 in illustration of it, two cases of transformation, of which 

 there is no doubt, the change from carbonic acid and water 

 to starch in the cells of plants (oxygen escaping), and the 

 change from starch to fat in the cells of animals (carbonic acid 

 and water escaping). And that I am correct in asserting 

 that the organ which exercises this and other chemical powers 

 in living plants is not only of the simplest construction, but 

 of uniform construction, while the products of its action are 

 very various, will appear from the following statement by 

 Mulder. 



" Pure cellulose is easily obtained from the pith of the elder- 

 tree, from very young roots, and from other young parts of 

 plants. From these parts it is prepared by digesting them, 

 after being minutely divided, with alcohol, ether, diluted pot- 

 ash, hydrochloric acid, and water. In this manner, the starch, 

 gum, fats, resins, vegetable alkalies, salts, sugar, — and at the 

 same time the peculiar woody matter, are separated." 



** After the action of these solvents, and especially of the 

 alkali, the cellulose, which was formerly solid and dense, ap- 

 pears in a spongy form. We may state as a tact, that the 



VOL. XLI. NO. LXXXII. — OCTOBER 1846. T 



