It is characteristic of this form of punishment, inspired by all that is pitiless, that is to say brutalizing, that gradually, by a process of mindless erosion, it turns a man into an animal, sometimes a ferocious one.
 
[Le propre des peines de cette nature, dans lesquelles domine ce qui est impitoyable, c’est-à-dire ce qui est abrutissant, c’est de transformer peu à peu, par une sorte de transfiguration stupide, un homme en une bête fauve, quelquefois en une bête féroce.]

Victor Hugo (1802-1885) French writer
Les Misérables, Part 1 “Fantine,” Book 2 “The Fall,” ch. 7 (1.2.7) (1862) [tr. Denny (1976)]
    (Source)

On the degradation of Jean Valjean while serving his hard labor sentence.

(Source (French)). Alternate translations:

The peculiarity of punishment of this kind, in which what is pitiless, that is to say, what is brutalising, predominates, is to transform little by little, by a slow stupefaction, a man into an animal, sometimes into a wild beast.
[tr. Wilbour (1862)]

The peculiarity of punishments of this nature, in which naught but what is pitiless, that is to say, brutalizing, prevails, is gradually, and by a species of stupid transfiguration, to transform a man into a wild beast, at times a ferocious beast.
[tr. Wraxall (1862)]

The peculiarity of pains of this nature, in which that which is pitiless -- that is to say, that which is brutalizing -- predominates, is to transform a man, little by little, by a sort of stupid transfiguration, into a wild beast; sometimes into a ferocious beast.
[tr. Hapgood (1887)]

The peculiarity of punishment of this kind, in which the pitiless or brutalizing part predominates, is to transform gradually by a slow numbing process a man into an animal, sometimes into a wild beast.
[tr. Wilbour/Fahnestock/MacAfee (1987)]

It is in the nature of such punishment -- in which what prevails is the pitiless, in other words, the brutalizing -- to transform a man little by little, by a kind of stupid transfiguration, into a wild beast, sometimes a ferocious beast.
[tr. Donougher (2013)]