OP THE BLOOD. GENERAL CONSIDERATIONS. 153 



completeness. The inferiority of nervo-muscular energy and of general vigor 

 are thus evidently the result of the deficiency, and not (as in the period of 

 growth) of the excess, of formative power ; and in proportion as the " waste" of 

 the tissues consequent upon their functional activity is more rapid than their 

 renovation, a progressive diminution must take place. It is obvious that the 

 cause of this decline must lie within the organism itself; since the external con- 

 ditions remaining the same, the same amount of vital activity is no longer mani- 

 fested ; and we can scarcely attribute it to any other source, than a gradual 

 decline in the "germinal capacity/ 7 which seems to set a limit to the life of the 

 entire organism, as it does to that of the single cell. For, when neither disease 

 nor accident shortens what may be considered the normal term of life, there is 

 a gradual diminution in every kind of vital activity, until it entirely ceases ; the 

 formative power seems progressively to exhaust itself, until no assistance from 

 artificial heat, no supply of the most nutritious food, can any longer avail for the 

 generation of new tissue; and the nervo-muscular energy gradually declines, 

 until at last even those actions on which the circulation and respiration entirely 

 depend can no longer be performed, and with the cessation of these functions the 

 life of the entire organism becomes extinct. Such we may consider to be the 

 mode in which Death normally occurs. Various abnormal influences, however, 

 may bring about this final result, at an earlier period, and in different modes; 

 these will be considered on a future occasion (CHAP. xxi.). 



CHAPTER IV. 



OP THE BLOOD; ITS PHYSICAL CHARACTERS, CHEMICAL 

 COMPOSITION, AND VITAL PROPERTIES. 



1. General Considerations. 



134. IN the organism of Man, as in that of all the higher Animals, the 

 materials for the nutrition of every portion of the structure are supplied by the 

 Blood, which, itself formed at the expense of the organic and inorganic constitu- 

 ents of the Food, is constantly circulating through the vessels during the whole 

 of life ; and each tissue possesses the power of drawing from this liquid, and of 

 appropriating to its own use, the particular components of its substance, which 

 either pre-exist as such in the blood, or are capable of being readily formed 

 from it by a process of chemical transformation. The supply of these materials, 

 however, is by no means the sole purpose of the Circulation of the Blood ; for it 

 also furnishes the means of removing the effete particles which are set free by 

 the disintegration of the tissues ; these being drawn into the current, probably 

 at the very time when the components of the newly-forming structures are given 

 forth, and being conveyed by it to the various organs which are provided for their 

 elimination. Hence the Blood not only contains the materials for the renovation 

 of the tissues, but also the products of their decay : but there is an important 

 difference in the proportion of these two sets of components ; for whilst the former 

 make up the principal part of the mass of the fluid, the latter are only detectable 

 in it with difficulty, so long as the excretory organs maintain their normal acti- 

 vity ; and only make their presence obvious, when they accumulate unduly, in 

 consequence of the retardation or suspension of the eliminating operations. 

 But besides thus meeting the demand occasioned by the constructive operations, 



