Navigating an object path, using a variable

1

lets say I have a variable like this:

var pathName = "section2";

Then I have an object called “book”. “book” is the parent of other objects named:
section1, section2, section3 and section4.

I want to apply a gotoAndStop() to section2 inside the book object. But instead of typing it the normal way:

_root.book.section2.gotoAndStop(2);

I want to use the variable pathName for this. Like so:

_root.book.pathName.gotoAndStop(2);

This is obviously not working, how can I use a variable as part of an object path navigation?

Thanks in advanced I hope someone here can help me !!! cheers