But the high development of the nervous system in man, its susceptibility to various influences, and the power of expression which man possesses - the very qualities which render him such a valuable subject for experiment make experiments upon him all the more liable to fallacy. Thus we find that in the experiments of Hein-rich and Dworzak aconite was found to cause neuralgic pains in the face; but unfortunately these observers have not mentioned whether any carious teeth were present, and so we cannot ascertain whether the neuralgia was due to the action of the aconite itself upon healthy nerves, or to alterations in the circulation of the alveoli lodging decayed teeth.

One of the most marked examples of the fallacies occurring in experiments upon man, and of the errors to which such fallacies may lead, is to be found in the provings which Hahnemann made of cinchona bark, and which led him to formulate the doctrine of homoeopathy. Hahnemann, for the sake of experiment, took for several days 4 drachms of good cinchona bark twice a day, and then began to suffer from all the ordinary symptoms of intermittent fever. On leaving off the drug he soon became quite well. He therefore concluded that cinchona bark, which was well known to be a remedy for ague, could also produce it.

Everyone who has an extended experience of ague knows well that even when patients have been free from any symptoms of the disease for a considerable length of time, they may be caused to reappear by various conditions, and more especially by anything that irritates the stomach or intestines. I have not myself seen a case of ague brought on by the administration of cinchona bark, but I have seen it occur after a succession of heavy dinners in a patient who had been long free from it. Powdered cinchona is certainly irritant, and Jorg found that in two-drachm doses it might cause flatulence, irritation, and nausea. Hahnemann took it in double this dose, and in all probability the ague which it brought on was simply due to gastric irritation, and not to any specific action of the cinchona. Had Hahnemann taken any other irritant which disagreed with him - say tartar emetic, or perhaps even pork-pie - he might have suffered in the same way, and yet pork-pie could hardly be said to be a specific for ague.