Cuvier, in his Animal Kingdom (trans. M’Murtrie):
Life then is a vortex, more or less rapid, more or less complicated, the direction of which is invariable, and which always carries along molecules of similar kinds, but into which individual molecules are continually entering, and from which they are continually departing; so that the form of a living body is more essential to it than its matter.
As long as this motion subsists, the body in which it takes place is living—it lives. When it finally ceases, it dies. After death, the elements which compose it, abandoned to the ordinary chemical affinities, soon separate, from which, more or less quickly, results the dissolution of the once living body. It was then by the vital motion that its dissolution was arrested, and its elements were held in a temporary union.
All living bodies die after a certain period, whose extreme limit is fixed for each species, and death appears to be a necessary consequence of life, which, by its own action, insensibly alters the structure of the body, so as to render its continuance impossible.
And Macleay, in his Horæ Entomologicæ:
Though for the sake of simplicity, and in order to avoid as much as possible what may be accounted as matter of opinion, death has in the foregoing paragraph been considered as merely the cessation of life ; yet it may be proper to observe, that those physiologists appear to have reason on their side, who make it generally an inevitable and necessary consequence of life. In the higher animals and plants, indeed, we are certain that if death should not be produced by accidental causes, it is sure in due time to result from the fibres which compose the cellular substance growing so thick and rigid, that the fluids cannot penetrate through their interstices. In this sense a body receiving nourishment may be said to imbibe death : so true it is, that by living we die.