OF VITAL ACTIONS, AND THEIR MUTUAL DEPENDENCE. 71 



or Vegetative life ; and they are subdivided into those concerned in the main- 

 tenance of the structure of the individual, which are termed functions of Nu- 

 trition, and those to which the Reproduction of the species is due. The 

 functions of Nutrition in Plants may be thus generally described. The first 

 step in the process, is the Absorption of nutriment from without. This is car- 

 ried by Circulation to the parts of the structure distant from those at which 

 it was absorbed. At some of these parts, the absorbed fluid is brought into 

 relation with the air, by which certain changes are effected in its constitution ; 

 these may be included under the general term deration, only a part of them 

 being analogous to the Respiration of Animals. Having undergone these 

 changes, and lost a considerable part of its superfluous water by the process 

 of Exhalation, the alimentary fluid is prepared to be applied to its various 

 purposes in the system ; and, being carried through the fabric by the Circu- 

 lation, it becomes subservient to the Nutrition and extension of the fabric, and 

 to the formation of various products of Secretion. It also affords the means, 

 to the organs of Reproduction, of the performance of their functions ; since 

 a new germ cannot be formed, any more than the parent structure can be ex- 

 tended, without organizable materials prepared by the foregoing processes, and 

 supplied to the parts where active changes are going on. 



76. On analyzing the operations which take place in the Animal body, we 

 find that a large number of them are essentially the same in character with 

 the foregoing, and differ only in the conditions under which they are per- 

 formed; and that we may, in fact, readily separate the Organic functions, 

 which are directly concerned in the riiaintenance of the fabric, from those of 

 Animal life, the chief purpose of which is entirely different. In commencing 

 the survey of these, we must revert to what has been already said in regard 

 to the nature of the food of Animals, and the means by which it is prepared 

 to be applied to the wants of their system ( 14). Not being received (in 

 general at least) in any but the solid form, it needs to be reduced to the fluid 

 state, before it can be introduced by absorption into the system: this reduction,, 

 which is termed Digestion, must be regarded as not merely a process of me- 

 chanical separation or solution, but as one of chemical change. By a part of 

 the same process, a certain degree of separation is effected, between that por- 

 tion of the reduced aliment which is fit for absorption and that which is not 

 adapted to serve any purpose in the economy ; and the latter, together with 

 certain products of secretion, which it is equally desirable to get rid of com- 

 pletely, is at once cast out of the system. The alimentary fluid is then taken 

 up by Absorption, through the vessels spread out upon the walls of the stom- 

 ach and intestinal tube, precisely in the same manner as it is received into 

 Plants through their roots distributed' in the soil: hence the earth has been not 

 unaptly designated as the common stomach of Plants ; and Animals have been 

 said to carry their soil about with them. The absorbed fluid, having been 

 introduced into the general current of the Circulation, is first carried to the 

 Respiratory organs, where it is exposed to the action of the air ; and it is then 

 transmitted to the system, for the purposes of Nutrition, Secretion, and Repro- 

 duction. So far, then, the functions of the Animal system coincide with those 

 of the Plant. The Organic functions of the former, however, have a purpose or 

 object superadded to that which they perform in the latter, Avhere their only 

 end seems to be the production and maintenance of the individual fabric, and 

 the continuance of the race. They are made subservient in Animals to those 

 functions by which they are peculiarly characterized, namely, Sensation 

 and Voluntary Motion ; all the instruments of these operations being main- 

 tained, like the rest of the organic structure, in a state fit for activity, by the 

 processes of Nutrition, which are performed on the same plan in them as in 

 other parts. 



