Griffith exposed weak living bacteria to just the fluids from dead virulent bacteria. some of these weak bacteria became virulent and could now kill mice. what control experiment did he do to argue that his weak bacteria changed to virulence in these studies?

This is more formally called the Avery-MacLeod-McCarty experiment. This experiment was done to demonstrate that bacterial transformation is caused by DNA. In Griffith's experiment, a rough strain of S. pneumoniae which is non-virulent which did not kill the mouse. A smooth strain of S. pneumoniae which is virulent killed the mouse. A heat-killed smooth strain of S. pneumoniae which was assumed to be non-virulent did not kill the mouse. However, the combination of a rough strain and a heat-killed smooth strain killed the mouse. This proves that the DNA from the heat-killed smooth strain lead to bacterial transformation of the rough strain into the smooth strain, therefore killing the mouse.