How to get bodytext of email

Dear Forum,

I have a message header in a variable:

var uriString = gFolderDisplay.selectedMessageUris;
var msgHdr = messenger.messageServiceFromURI(uriString)
.messageURIToMsgHdr(uriString);

I can get author and subject directly from the msgHdr object, but I cannot seem to find a way to get the bodytext.

Could you give me a hint where to look?
I really appreciate your help!