The film wanted to point out conditions in prisons and their main failure. Instead of helping the prisoners to develop a feeling for having done wrong and towards re-integration into society (as prisons are supposed to do) they achieve actually the opposite: even prisoners, who are halfway civilized when entering, quickly learn the law of the jungle, if they want to survive in prison. That is what the title means. But somehow, I can't help cheering Franz for beating the thugs at their own game, instead of regretting his loss of morals!!
This character-study-of-prisoners (and study of the prisons themselves) is done all the time and I didn't see anything new in this one, but was quite pleased with it; of the Prochnow German movies of the early-to-mid 70's this is the one I would pick to watch a few times over again. The characters were all interesting; the cast was swell; and it gave Jürgen a chance to do some fabulous acting. I got hooked up front with the going-nuts-in-the-cell scene where he screams and cries and trashes the room, which I might have laughed at as overacting in other circumstances, but it the feeling was all too real here - I was worried about the guy! You can also put this right up there with DIE WILDNIS for genuinely horrifying brutality, as the beating scenes are no joke either, and a little too well done; I almost had to watch some of that through my fingers.
You see Franz's personality change as he goes from despair to determination and it's beautifully played out by Jürgen, with excellent support from the cast - I especially liked his weasely little buddy. It's a rough movie, but well worth seeing.