220 GENERAL VIEW OF THE FUNCTIONS. 



preparation, and for their maintenance in the requisite state of purity, that a 

 large part of the fabric of the Animal is destined. But if we could imagine 

 its several tissues to be supplied with nutriment in any other manner, and 

 maintained in other respects in their normal circumstances (as regards warmth, 

 air, &c.), we have every reason to believe that their independent vitality would 

 manifest itself by their continued development, and by the regular exhibition 

 of their ordinary properties. An approach to this condition is made, in the 

 experiment of entirely detaching a limb from the body, but keeping up the 

 circulation of blood through it, by means of tubes connecting its main artery 

 and vein with those of the stump. Notwithstanding the prejudicial effect of 

 such severe injuries, the increased duration of the muscular irritability in the 

 separated part, is a sufficient proof of the continuance of the normal actions of 

 nutrition, although of course in a diminished degree. And the occasional 

 reunion of a member which has been entirely separated, when decomposing 

 changes have not yet commenced in it, most clearly shows, that nothing but 

 the restoration of its supply of nutriment is requisite for the preservation of 

 its vitality, and that its powers of growth and renovation are inherent in itself, 

 only requiring a due supply of the nutrient material, with certain other con- 

 current conditions. 



260. In every living structure of a complex nature, therefore, we see a great 

 variety of actions, resulting from the exercise of the different properties of its 

 several component parts. If we take a general survey of them, with reference 

 to their mutual relations to each other, we shall perceive that they may be 

 associated into groups; each consisting of a set of actions, which, though 

 different in themselves, concur in effecting some positive and determined pur- 

 pose. These groups of actions are termed Functions. Thus, one of the 

 most universal of all the changes necessary to the continued existence of a 

 living being, is the exposure of its nutritious fluid to the air; by the action of 

 which upon it, certain alterations are effected. For the performance of this 

 aeration, simple as the change appears, many provisions are required. In the 

 first place, there must be an aerating surface, consisting of a thin membrane, 

 permeable to gases; on the one side of which the blood may be spread out, 

 whilst the air is in contact with the other. Then there must be a provision 

 for continually renewing the blood which is brought to this surface; in order 

 that the whole mass of fluid may be equally benefited by the process. And, 

 in like manner, the stratum of air must also be renewed, as frequently as its 

 constituents have undergone any essential change. We include, therefore, in 

 speaking of the Function of Respiration, not only the actual aerating process, 

 but also the various changes which are necessary to carry this into effect, and 

 which obviously have it for their ultimate purpose. 



261. On further examining and comparing these Functions, we find that 

 they are themselves capable of some degree of classification. Indeed the dis- 

 tinction between the groups into which they may be arranged, is one of essen- 

 tial importance in Animal Physiology. If we contemplate the history of the 

 Life of a Plant, we perceive that it grows from a germ to a fabric of sometimes 

 gigantic size, generates a large quantity of organised structure, as well as 

 many organic compounds, which form the products of secretion, but which do 

 not undergo organization, and multiplies its species, by the production of 

 germs similar to that from which it originated; but that it performs all these 

 complex operations, without (so far as we can perceive) either feeling or think- 

 ing, without consciousness or will. All the functions of which its Life is com- 

 posed, are, therefore, grouped together under the general designation of Func- 

 tions of Organic or Vegetative life: and they are subdivided into those con- 

 cerned in the maintenance of the structure of the individual, which are termed 

 functions of Nutrition; and those to which the Reproduction of the species 



