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PHYSIOLOGY. 



The continual death, or destruction of the individual cells which 

 enter into the composition of the organs or tissues, constitutes what 

 is called, molecular deaths to distinguish it from somatic deaths or 

 the death of the ivhole body, which follows upon the cessation of the 

 respiratory and circulatory functions. Molecular death, however, is 

 not always an immediate result of somatic death, since it is known 

 that the lives of individual parts may be prolonged after the suspen- 

 sion of the regular series of their combined operations ; so on the 

 other hand, molecular death may take place to a considerable extent, 

 if the function of the part have no immediate relation to the indis- 

 pensable actions just alluded to, without somatic death necessarily 

 resulting. 



There is no valid reason for believing that the processes of nutri- 

 tion are dependent upon nervous influence, although, as before stated, 

 it is known that they may be influenced by it. These processes go 

 on with great regularity and rapidity in the vegetable kingdom, in 

 which nothing approaching to a nervous system exists ; and in the 

 animal kingdom they take place long before any nervous system be- 

 gins to be developed ; the conversion of the primary cells into mus- 

 cular tissue, bone, and mucous membrane takes place in virtue of the 

 inherent properties of the primary tissue itself, since no nervous 

 influence can be supposed to operate, before nerves are called into 

 existence. 



SECRETION. 



Nearly allied to the function last considered (nutrition) is that of 

 secretion, which means literally separatioii. In both certain materials 

 are separated from the blood ; in nutrition the object of the separa- 

 tion is to build up the living body ; in secretion, to get rid of certain 

 useless substances, or to supply certain other combinations that may 

 either directly or indirectly be essential to the economy. 



The essential character of the true secreting process seems to con- 

 sist not so much in the nature of the action itself, for this is identical 

 with that of nutrition, both being effected by a process of cell-growth, 

 but in the position in which the cells are developed, and the manner 

 in which their products are disposed of. In secretion the product of 

 the action of the cells is delivered upon a free surface, communicating, 

 more or less directly, with an external outlet, or into cavities pro- 

 vided with orifices that lead to them. 



The organs by which the latter operations are effected, are called 

 secreting organs, and the matters separated are spoken of as secreted 

 fluids, or simply as secretions. 



A distinction has been made between those secretions that are 

 produced with an ulterior view as means to other functions in the 

 economy, such as the saliva, gastric juice, &c., and those that are 

 immediately rejected from the organism, as useless, as for example, 



