How does Bruce persuade the Motilones to use disinfectants?

Bruce persuades the Motilones to use disinfectants. First he shows the witch doctor the germs under a microscope. The witch doctor tries using her incantations, but they do not kill the germs. When Bruce uses antispetic, the germs die. Over a period of time the witch doctor introduces disinfectants when a new communal home is built and when babies are born.