INFLUENCE OF THE NERVOUS SYSTEM, ETC. 941 



CHAPTER XVIII. 



INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC 

 FUNCTIONS. 



945. OF the modes in which the Nervous System influences the Organic 

 Functions, a great part have been already considered : for it has been shown to 

 be concerned in providing the conditions, either immediate or remote, under 

 which alone these functions can be performed ; so that, when its activity ceases, 

 they cannot be much longer maintained. But the influence of the Nervous 

 System is not alone exerted upon the motor or contractile tissues of the body; 

 for there is good evidence that it has a direct operation upon the molecular 

 changes which constitute the functions of Nutrition, Secretion, &c. ; and it is 

 quite conformable to the general views formerly expressed (CHAP, in.) respect- 

 ing the relations of the different kinds of Vital Force, that the nerve-force, which 

 is itself generated by cell-development, should in its turn be able to modify other 

 processes of cell-development ( 111). And this view may be admitted to its 

 fullest extent, without our thereby being led to regard the processes in question 

 as dependent upon Nervous agency a doctrine for which there seems no valid 

 foundation, since they go on with the greatest rapidity and energy in the Vege- 

 table kingdom, in which nothing approaching to a Nervous System exists ; whilst 

 in the Animal kingdom they take place with equal vigor, long before the least 

 vestige of it appears. We shall see that in the earliest condition of foetal life, 

 the germ consists but of a congeries of cells, which have all originated in a. single 

 one ( 993) ; and from this mass, the several tissues and organs are successively 

 generated by the processes of histological and morphological transformation one 

 set of cells being converted into muscular tissue, another into nervous tissue, 

 another into mucous membrane, and so on. Now since this is the case, it is 

 evident that all these processes of development must take place, in virtue of the 

 inherent properties of the primitive substance itself; since no nervous influence 

 can be supposed to operate before nerves are called into existence. Throughout 

 the Animal body, it may be observed that the more Vegetative the nature 

 of any function, the less is it connected with the Nervous System ; and all the 

 experiments which have been regarded as proving that the Organic functions 

 are dependent upon Nervous influence, are really explicable, fully as well, upon 

 the supposition that they are capable of being affected by it, either in the way of 

 excitement or retardation. (See 447.) Moreover, there is abundant evidence 

 that Secretion may take place after the death of the general system, through the 

 persistence of certain molecular changes whose essential conditions are not 

 immediately altered; thus, Mr. T. Bell mentions that, in dissecting the poison- 

 apparatus of a Rattlesnake which had been dead for some hours, the poison con- 

 tinued to be secreted so fast as to require being occasionally dried off. This is 

 precisely what might have been anticipated, from the independent power of growth 

 in the secreting cells; and other acts of Nutrition are recorded to have occurred 

 under similar circumstances. In such a case, the Animal body is reduced to 

 the condition of a Plant; since the influence of the Nervous system must then 

 be entirely extinct. Upon those who maintain that Nervous agency is a condi- 

 tion essential to those molecular actions of which Nutrition and Secretion consist, 



