this code doesn't work... why?
how can i add that head to that body?

head is the html text i want to add to p (a tmail object)

 def injecthead(head,p)
      if p.multipart? then
        p.parts.each do |pa|
          injecthead(head,pa)
        end
      else
        if p.content_type=="text/html" then
          if p.body!=nil then
            startbodytag=p.body.index("<body")
            endbodytag=(p.body[startbodytag...p.body.length]).index(">")
            if startbodytag!=nil then
              p.body.insert(startbodytag+endbodytag+1,head)

              #i'm sure this code is worked but p.body doesn't change.
              #if i put 
altbody=p.body.insert(startbodytag+endbodytag+1,head),
              #altbody is the body i want, but if then i write 
p.body=altbody, p.body becames nil

            end
          end
        end

      end
    end