FRANKFURT, June 29 (Reuters) - German engineering conglomerate Siemens AG (SIEGn.DE: Quote, Profile, Research) will bulk up its medical business by buying the diagnostics unit of drugs and chemicals group Bayer AG (BAYG.DE: Quote, Profile, Research) for 4.2 billion euros ($5.3 billion). The acquisition, the second major purchase by Siemens' thriving healthcare unit in two months, will make Siemens the world's second largest player in immunodiagnostics, the science of using specific antibodies to diagnose diseases, it said on Thursday.
