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the principle belonging to the preparatory structures may be con- 

 sumed in separating from the fluid destined for nutrition hetero- 

 geneous substances or properties; or, 2nd, that the living properties 

 of the textures passing into the fluids destined for nutrition, and 

 becoming again informal life, may determine the due relation be- 

 tween the nutrient material and the peculiar nature which it is 

 destined to support. 



15. Whatever the precise nature of these curious processes 

 may be (and which, for want of the sense which we have so often 

 alluded to, we shall never understand) this law appears common and 

 universal to the living specimens of both kingdoms, viz. that though 

 an immense variety of animals (and vegetables) of the same genus 

 may derive their support from the same aliment, yet the condition 

 upon which the life and corporeal character of each are maintained 

 is, that the aliment for such purposes should undergo a preparation 

 by the organs of the living form which it is destined to nourish; 

 nay, so essentially and peculiarly is the function of the preparatory 

 organs related with the diffused life and textures, that blood itself, 

 from an animal of the same species, thrown into the system of the 

 circulation, will not prove a substitute for that fluid whose proper- 

 ties are endowed by organs, in conformity with a natural and 

 specific relation.* To this general view we shall perhaps have oc- 

 casion to return. Having shewn the necessity of the operation of 

 the living principle belonging to these organs, we are next to con- 

 sider the laws which belong to the principle itself, or at least to 

 exhibit some alternatives respecting it. 



16. We have seen that the operation of the organic spirit be- 

 longing to the structure of the intestines is either direct or through 

 the medium of the fluids supplied to the chyme. There is a de- 

 ficiency of facts to prove whether indeed the former mode occurs 

 at all, though, for the reasons stated, it appears probable. It is now 

 to be inquired, 1st, whether those spiritual properties which are 

 engaged in the conversion are those of the assimilating life; or, 

 2nd, whether they are that conjoined result which we have ex- 

 pressed " the regular dependent;" or, whether they are of the 



* The only instances of nutrition by a material prepared by foreign 

 organs are those exemplified in the engrafting of animal and vegetable sub- 

 stances. In these cases, the life of the foreign substance mnst in its proper- 

 ties and constitution so far resemble that of the substance with which it is 

 united, that the material which is prepared for one agrees with common pro- 

 perties of both. When substances are in this way united, the foreign or 

 additional one commonly preserves its own character, or takes only itself out 

 of a material which possesses its properties as well as those of the organiza- 

 tion with which it is allied. In such cases, the affinity betweeu the substances 

 is only of resembling properties, without constitution or the production of a 

 differential. In other cases which are perhaps exceptious, the growth and 

 product of the foreign substance is modified by its new connexion. In this 

 case there is not only an union of common properties, but communion of other 

 related ones giving rise to change, or constitution: as in generation, some 

 properties of the parents mix and modify each other, and some preserve their 

 separate and original character. 



