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A substance has been demonstrated in acetone extracts of freeze-dried spleen which had cardiotonic properties on isolated papillary muscles from the cat and perfused hearts of the cat and guinea-pig. This activity of the extract could not be explained by the presence of choline, acetylcholine, histamine, 5-hydroxytryptamine, adrenaline or noradrenaline.
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Cobbin et al. (1959) studied this question.
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