Abstract
Ways in which chemical techniques could be applied to the understanding of neural systems, their functioning and their disorders were devised only gradually during the present century. In a particularly successful procedure, now termed assay-guided isolation, neural defects were made good by means of tissue-extracts and the restoration of function was established as an assay-system to guide the chemical separation and identification of the active tissue constituent. Thiamin was so isolated, using an experimental polyneuritis assay; subsequent instances among other metabolites, hormones, neurotransmitters and nerve growth factors are recounted. Procedures of assay-guided characterization ensured that links were retained between specific, sparsely-occurring substances and chosen aspects of their biological roles while their chemical nature was first explored and then established. The procedures discouraged the too-facile postulating of hypothetical molecules and contributed to the distinctiveness of neurochemistry as a subject within the neurosciences.
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