Fluorescence microscopy assumed a pivotal role in cell biology once it was possible to stain cell components selectively by fluorescing dyes. One of the first explorers of targeted stainings, Paul Ehrlich, had the idea that something that stains specifically should also kill specifically – which was associated with the term “magic bullet”, the essential idea of chemotherapy. His group discovered Salvarsan, a tailored drug against syphilis – though not specific enough not to cause substantial side effects. Screening many fluorescent dyes led to a long list of stainings which are used in histology, including dyes like DAPI or hematoxylin and eosin.