12
men of high attainment of our own day could copy such an example. Galen held correctly that the heart, though unlike other muscles was still muscular in its action; he knew the structure of the valves of the heart, but he affirmed that there were pores in the septum between the ventricles which allowed some of the blood to pass from the right to the left side of the heart. Here he asserted what reason fancied rather than what he learnt by direct observation-a lesson to us, even at the present day, of the danger of form- ing our opinions on hypotheses rather than on established facts. Reason affirms that such and such things are true, but further observation subsequently dis- proves them. How slow we are to learn this lesson, but how disastrous has been the result, when the statements of reason are received as facts, and are regarded as solid bases upon which scientific truths may be built; for like buildings upon unstable foundations they crumble and decay when really tested. It is a slow process to get rid of these
