Instruction from Paul Ehrlich to Henry Dale (later Sir Henry). At the time Dale was working in Ehrlich's laboratory. The cards bearing notes or instructions were known as blocks

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Instruction from Paul Ehrlich to Henry Dale (later Sir Henry). At the time Dale was working in Ehrlich's laboratory. The cards bearing notes or instructions were known as blocks. Wellcome Collection. Attribution 4.0 International (CC BY 4.0). Source: Wellcome Collection.