Adding a new line to a TextBlock if necessary

I read JSON from WebService and put my data in a list of text blocks (wrapped in grids). Sometimes the text is long, and I would like the text block to automatically add a new line (if not necessary, and on the right - endlessly).

I read somewhere that I should put a text block in a shortcut (not recognized VS2010?) ..

I can’t put <\ newline> or \ n or anything, because I don’t know where and when.

Thank.