FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 231 



the proper contractility of these, which (like that of the heart and alimentary 

 canal) is directly stimulated by the contact of their contents; but there is 

 also evidence that this contractility may be affected (as it is in those two 

 instances) by the nervous system; and thus we have an additional means of 

 influence, by which the nervous system can operate on these processes, since 

 its power is probably not confined to the large ducts, but extends to their 

 ultimate ramifications. Where, as happens in the case of the urinary excre- 

 tion, there is a reservoir into which it is received as fast as it is formed, for 

 the purpose of preventing the inconvenience which its constant passage from 

 the body would otherwise occasion, the power of emptying this reservoir is 

 usually placed in some degree under the dominion of the will, although 

 chiefly governed by reflex action. It is obvious that such a provision is by 

 no means essential to the function; and that it has for its object the adapta- 

 tion, merely, of that function, to the conditions of Animal existence. 



280. Thus we see that, when we enter, as it were, into the penetralia of 

 the Animal system, and study those processes, of which the development and 

 maintenance of the material fabric essentially consist, we find them performed 

 under conditions essentially the same as those which obtain in Plants ; and 

 we observe that the operations of the Nervous System have none but an 

 indirect influence or control over them. It is, therefore, quite philosophical 

 to distinguish these Organic Functions, or phenomena of Vegetative Life, 

 from those concerned in the Life of Relation, or Animal Life. The distinc- 

 tion is, indeed, of great practical importance, and lies at the foundation of all 

 Physiological Science; yet it is seldom accurately made, and a very confused 

 notion on the subject is generally prevalent. It is commonly said, for ex- 

 ample, that the function of Respiration is the connecting link between the 

 two: the fact being, however, that the true process of Respiration is no 

 more a function of Animal life, than is any ordinary process of secretion ; but 

 that, in order to secure the constant interchange of air, which is necessary to 

 its performance, the assistance of the nervous and muscular systems is called 

 in, though not in a manner which necessarily involves either consciousness 

 or will. 



281. The process of Reproduction, like that of Nutrition, has been until 

 recently involved in great obscurity ; and although it cannot be said to be _vet 

 fully elucidated, it has been brought, by late investigations, far more within 

 our comprehension, than was formerly deemed possible. The close connec- 

 tion between the Reproductive and Nutritive operations, both as regards their 

 respective characters, and their dependence upon one another, has long been 

 recognized; and it is now rendered still more evident. Nutrition has not been 

 unaptly designated " a perpetual reproduction;" and the expression is strictly 

 correct. In the fully-formed organism, the supply of alimentary material to 

 every part of the fabric, enables it to produce a tissue resembling itself; thus 

 we only find true bone produced in continuity with bone, nerve with nerve, 

 muscle with muscle, and so on. Hence it would appear that, when a group 

 of cells has once taken on a particular kind of development, it continues to 

 reproduce itself on the same plan. But in the Reproductive process it is 

 different. A single cell is generated by certain preliminary actions, from 

 which single cell, all those which subsequently compose the embryonic struc- 

 tures, take their origin ; and it is not until a later period, that any distinction 

 of parts can be traced, in the mass of vesicles which spring from it. Hence 

 the essential character of the process of Reproduction consists in the forma- 

 tion of a cell, which can give origin to others, from which again others spring ; 

 and in the capability of these last to undergo several kinds of transforma- 

 tion, so as ultimately to produce a fabric, in which the number of different 

 parts is equal to that of the functions to be performed, every separate part 



