As the war goes on, how are the changes in the trench similar to the changes in the soldiers?

Basically as the war goes on the trenches become rat infested, disease ridden pits of death. The morale of the soldiers also breaks down.

"Katczinsky is right when he says it would not be such a bad war if only one could get a little more sleep. In the line we have next to none, and fourteen days is a long time at one stretch. "

"Iron Youth. Youth! We are none of us more than twenty years old. But young? Youth? That is long ago. We are old folk." pg 5