76 GENERAL VIEW OF THE FUNCTIONS. 



interruption of the circulation, than will the Nervous structure, which is, in- 

 deed, instantaneously affected by a cessation of the due supply of blood, or by 

 the depravation of its quality. 



82. It is of little consequence, then, with which group of functions we com- 

 mence the detailed study of the phenomena which, in their totality, make up 

 the life of Man. In viewing him merely as one of the widely-extended group 

 of organized beings, it would be natural to commence with those phenomena 

 which are common to all ; and to make, therefore, the Organic functions the 

 first object of our consideration. On the other hand, regarding Man as a being 

 in some degree isolated from all these by his peculiar characteristics, it seems 

 right to inquire into the latter in the first instance ; more especially as, in a 

 general view of his life, these occupy the most prominent place. It will be 

 necessary, however, previously to entering upon them, to take a more detailed 

 survey than we have hitherto done, of the vital operations performed by his 

 several organs, and of their connections with each other. We shall commence 

 with those of Vegetative Life. 



Functions of Vegetative Life. 



83. It is one of the most peculiar characteristics of organized structure, that 

 its elements have a constant tendency (under ordinary circumstances at least) 

 to separate into more simple combinations ; and, although it has been ordina- 

 rily considered that their living state prevents such a change, and that they 

 have no. tendency to it except when dead, reason will hereafter be given for 

 the belief that no such distinction exists ( 645, 646). The maintenance of 

 the vital properties of all organized structure, then, requires either that this 

 structure should be completely secluded from air, moisture, warmth, and other 

 agents which tend to its decomposition ; or that it should be renewed as fast 

 as it decays. Now the exclusion of these decomposing agents would prevent 

 any vital actions from being called into operation ; since they are the ordinary 

 stimuli, which are necessary to them. For instance, a seed which is buried 

 so deep in the soil as to be excluded from the contact of air, and from the 

 warmth of the sun, will not vegetate, although it may retain its power of germi- 

 nating when placed in more favourable circumstances ; and it will not decay, 

 because secluded from the air and warmth which are necessary to its decom- 

 position. But as a certain decomposition appears to be a necessary condition 

 of its vital activity, it is obviously necessary that a provision should be made, 

 for removing from the organism all those particles, which are manifesting an 

 incipient tendency to decay, and are thus losing their vital properties ; and for 

 replacing these by newly-combined particles, which in their turn undergo the 

 same process. Thus we find that, in the softest parts of the Animal frame- 

 work, as in those of the Plant, there is much less permanency than there is 

 in those harder and more solid portions, which often seem altogether to defy 

 the lapse of time. Now it is in the former that the most active vital changes 

 take place, those of the nervous system, for example ; whilst of the latter, the 

 function is chiefly, if not entirely, that of giving mechanical support to the 

 structure. The fact, which is easily proved, that the former organs are renewed 

 many times, whilst the fabric of the latter is not once completely changed, 

 shows a very interesting correspondence between the degree in which the 

 action of any organized structure is removed from, or is similar to, that of a 

 mere inorganic substance, and the amount of tendency to decomposition which 

 that structure exhibits ; since this constant renewal can scarcely serve any 

 other purpose than that of making up for the effects of decay. 



84. One of the most important purposes of the supply of aliment, therefore, 

 which all living beings continually require, is the replacement of the portions 



