Unlike the mechanical physicians, the chemists explain the beneficial operation of iron by supposing that it increases the proportion of red globules in the blood, on the erroneous[42] hypothesis that iron constitutes the principal element of these bodies. Thus has iron, from its acknowledged powers, been enlisted into the service of every prevailing hypothesis; and it is not a little singular, as a late writer has justly observed, that theories however different, and even adverse, do nevertheless often coincide in matters of practice, as well with each other as with long established empirical usages, each bending as it were, and conforming, in order to do homage to truth and experience. And yet iron, whose medicinal virtues have been so generally allowed, has not escaped those vicissitudes in reputation which almost every valuable remedy has been doomed to suffer: at one period the ancients imagined that wounds inflicted by iron instruments, were never disposed to heal, for which reason Porsenna, after the expulsion of the Tarquins, actually stipulated with the Romans that they should not use iron, except in agriculture; and Avicenna was so alarmed at the idea of its internal use as a remedy, when given in substance, that he seriously advised the exhibition of a magnet[43] after it to prevent any direful consequences. The fame even of Peruvian bark has been occasionally obscured by the clouds of false theory some condemned its use altogether, “because it did not evacuate the morbific matter,” others, “because it bred obstructions in the viscera,” others again, “because it only bound up the spirits, and stopped the paroxysms for a time, and favoured the translation of the peccant matter into the more noble parts.” Thus we learn from Morton,[44] that Oliver Cromwell fell a victim to an intermittent fever, because the Physicians were too timid to make a trial of the bark. It was sold first by the Jesuits for its weight in silver;[45] and Condamine relates that in 1690, about thirty years afterwards, several thousand pounds of it lay at Piura and Payta for want of a purchaser. Nor has Sugar escaped the venom of fanciful hypothesis. Dr. Willis raised a popular outcry against its domestic use, declaring that “it contained within its particles a secret acid—a dangerous sharpness,—which caused scurvys, consumptions, and other dreadful diseases.”[46]