724 HANDBOOK OF PHYSIOLOGY. 



putting off also of so much life ; and, apart from disease, the reverse 

 is true also. A living being starts on its career with a certain amount 

 of work to do varying infinitely in different individuals, but for each 

 well-defined. In the lowest members' of both the animal and vegetable 

 creation the progress of life in any given time seems to depend almost 

 entirely on external circumstances ; and at first sight it seems almost 

 as if these lowly-formed organisms were but the sport of the surrounding 

 elements. But it is only so in appearance, not in reality. Each act of 

 their life is so much expended of the time and work allotted to them ; 

 and if, from absence of those surrounding conditions under which alone 

 life is possible, their vitality is stayed for a time, it again proceeds on 

 the renewal of the necessary conditions, from that point which it had 

 already attained. The amount of life to be manifested by any given in- 

 dividual is the same, whether it takes a day or a year for its expenditure. 

 Life may be of course at any moment interrupted altogether by disease 

 and death. But supposing it, in any individual organism, to run its 

 natural course, it will attain but the same goal, whatever be its rate of 

 movement. Decline and death, therefore, are but the natural termina- 

 tions of life ; they form part of the conditions on which vital action 

 begins ; they are the end towards which it naturally tends. Death, not 

 by disease or injury, is not so much a violent interruption of the course 

 of life, as the attainment of a distant object which was in view from the 

 commencement. 



In the period of decline, as during growth, life consists in continued 

 manifestations of transformed physical force ; and there is of necessity 

 the same series of changes by which the individual, though bit by bit 

 perishing, yet by constant renewal retains its entity. The difference, as 

 has been more than once said, is in the comparative extent of the loss 

 and reproduction. In decline there is not perfect replacement of that 

 which is lost. Eepair becomes less and less perfect. It does not of 

 necessity happen that there is any decrease of the quantity of material 

 added in the place of that which disappears. But although the quantity 

 may not be lessened, and may indeed absolutely increase, it is not per- 

 fect as material for repair, and although there may be no wasting, there 

 is degeneration. 



No definite period can be assigned as existing between the end of de- 

 velopment and the beginning of decline, and chiefly because the two 

 processes go on side by side in different parts of the same organism. 

 The transition as a whole is therefore too gradual for appreciation. But, 

 after some time, all parts alike share in the tendency to degeneration; 

 until at length, being no longer able to subdue external force to vital 

 shape, they di ; and the elements of which they are composed simply 

 employ what remnant of power, in the shape of chemical affinity, is still 

 left in them, as a means whereby they may go back to the inorganic 



