OF DEGENERATION AND DEATH. 53 



ration to the mineral world, of the carbonic acid, water, and ammonia, 

 which have been appropriated by Plants ; and it will hereafter appear, 

 that the amount thus given off by the animal organism bears a close 

 correspondence, on the one hand, with its degree of vital activity, as 

 shown in the amount of heat and motion which it generates, and, on the 

 other, with the amount of the organic compounds which it consumes as 

 food. So that, on the whole, there is strong reason to believe that tEe 

 entire amount of force (as of materials), received by an animal during 

 a given period, is given back by it during that period, provided that its 

 condition at the end of the term is the same as it was at first ; and fur- 

 ther, that all the force (like the material), which has been expended in 

 the building up of the organism, is given back by its decay after death.* 



4. Of Degeneration and Death. 



64. We have seen that the general history of the phenomena of Life 

 is fully conformable with the view, that the Vital properties of a tissue 

 (that is, the properties in virtue of which the forces that act upon it 

 are caused to manifest themselves in Vital action), are dependent upon 

 that state of combination and arrangement, which is termed Organiza- 

 tion. As long as each tissue retains its normal or regular constitution, 

 renovated by the actions of absorption and deposition through which 

 that constitution is preserved, and surrounded by those other conditions 

 which a living system alone can afford, so long, we have reason to be- 

 lieve, it will retain its vital properties, and no longer. And just as 

 we have no evidence of the existence of vital properties in any other 

 form of matter than that which we call organized, so have we no reason 

 to believe that organized matter can retain its regular constitution, and 

 be subjected to the appropriate forces, without exhibiting vital actions. 

 The advance of pathological science renders it every day more probable 

 (indeed the probability may now be said to amount to almost positive 

 certainty), that derangement in function, in other words, an imperfect 

 or irregular action, always results, either from some change of struc- 

 ture or composition in the tissue itself, or from some corresponding 

 change in the forces by which the properties of the organ are called 

 into action. Thus, when a Muscle has been long disused, in can scarcely 

 be excited to contraction by the usual stimulus, or may even be altoge- 

 ther powerless ; and minute examination of its structure shows it to have 

 undergone a change, which is obvious to the microscope, though it may 

 not be perceptible to the unaided eye, and which results from imperfect 

 nutrition. Or, again, convulsive or irregular actions of the Nervous 

 system may be produced, not by any change in its own composition, 

 but by the presence of various stimulating substances in the blood, 

 although their amount be so small that they can scarcely be recognised. 

 ^ 65. As there is a constant tendency, in the Animal tissues more espe- 

 cially, to spontaneous decay, so must the maintenance of the vital pro- 



* The whole of this subject is more fully developed in the Author's "Principles of 

 Physiology, General and Comparative," CHAPS, m. and v. ; and in a Paper on " The 

 Mutual Relations of the Vital and Physical Forces," contained in the Philosophical 

 Transactions for 1850. 



