Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 24 & 25

24
Generation is the initial participation, mediated by warm substance,in the nutritive soul, and life is the maintenance of thisparticipation. Youth is the period of the growth of the primaryorgan of refrigeration, old age of its decay, while the interveningtime is the prime of life.A violent death or dissolution consists in the extinction orexhaustion of the vital heat (for either of these may causedissolution), while natural death is the exhaustion of the heatowing to lapse of time, and occurring at the end of life. In plantsthis is to wither, in animals to die. Death, in old age, is theexhaustion due to inability on the part of the organ, owing to oldage, to produce refrigeration. This then is our account ofgeneration and life and death, and the reason for their occurrencein animals.

25
It is hence also clear why respiring animals are suffocated in waterand fishes in air. For it is by water in the latter class, by air inthe former that refrigeration is effected, and either of these meansof performing the function is removed by a change of environment.There is also to be explained in either case the cause of thecause of the motion of the gills and of the lungs, the rise and fallof which effects the admission and expulsion of the breath or ofwater. The following, moreover, is the manner of the constitution ofthe organ.