The macroscopical and the microscopical researches on the pathology of the brain, in insanity and other neuroses, though hitherto carried on with zest to an almost unlimited extent, have yet been devoid of any very definite trustworthy results. Nor is this to be wondered at when we consider that infinitesimal particles, acting on the nervous system, are capable of producing very decided effects. Thus, a distinct sensation of smell is produced by so small a quantity of odorous particles as to be practically immeasurable. Therefore, the wonder is, as Dr. Maudsley observes, that any morbid appearances should have been expected to be found in many cases of insanity.