Just as the ties recur beneath his train, these underliehis rushing brain. (35-36)
There's a great rhythm here created by Bishop's words. In fact, most of the line is written in iambs, which mimics the sound of a train perfectly. The rhythm allows us just the tiniest glimpse of what's going on in the Man-Moth's head and what drives him to try and try again.
[...] He regards it as a diseasehe has inherited the susceptibility to. He has to keephis hands in his pockets, as others must wear mufflers. (38-40)
The temptation to give up lives in all of us, because sometimes it's just plain easier to believe we can't do it and walk away. The Man-Moth acknowledges this, but he considers it a disease, a thing to be prevented at all costs. If it means that he has to keep his hands in his pockets when the temptation is near, so be it. On the up side, he'll save a little cash since he won't have to buy mittens.