ACT II, SCENE 5, LINES 105-111
"Yea, from the table of my memory
I'll wipe away all trivial, fond records,
All saws of books, all forms, all pressures past,
That youth and observation copied there,
And thy commandment all alone shall live
Within the book and volume of my brain,
Unmixed with baser matter."

Hamlet wants to wipe his memory clean, as one would erase a slate.  All of the images he has of his mother and uncle are insignificant to him now in the face of their betrayal.  He will erase those images in his memory so as to not be deceived again.  With his memories erased, Hamlet will be able to properly avenge his father's murder. 

There are many images of sickness, disease, wickedness, blemishes on the body, and other loathsome things that are metaphorically descriptive or the unwholesome condition of Denmark.  Examples of this are on most pages.  A few examples are found in the following places:
3.4.43
4.5.18
3.4.74
1.4.27

ACT IV, SCENE 4, LINES 28-30
"This is th' impostume of much wealth and peace,
That inward breaks and shows no cause without
Why the man dies."

Hamlet is talking to Fortinbras' captain about the land, which has been symbolically given to Norway to prevent them from invading Denmark.  This statement is however, also descriptive of Hamlet's own condition.  The events that have caused his madness fester inside him like an abscess or tumor.  The cause is unseen by others though it is destroying him inside.