Of the hereditary transmission of idiotcy we naturally have not the same kind of evidence. Madness often, if not generally, comes on or shows itself late in life, whereas idiotcy is not often developed in the adult. Insanity is the diseased or weakened condition of a mind possessing all the ordinary thinking faculties; idiotcy implies that some of these faculties are altogether wanting. It has been asserted, by the way, that idiotcy is a product of civilisation. The civilised 'present, as peoples,' says Dr. Duncan, 'indications of defective vital force, which are not witnessed among those human beings that live in a state of nature. There must be something rotten in some parts of our boasted civilisation: and not only a something which has to do with our psychology, but a great deal more with our power of physical persistence. It is a fact that the type of the perfect minded, just above the highest idiots, or the simpletons, is more distinguishable amongst the most civilised of the civilised than among those who are the so-called children of nature. Dolts, boobies, stupids, _et hoc genus omne_, abound in young Saxondom; but their representatives are rare amongst the tribes that are slowly disappearing before the white man.' But it seems barely possible that the difference may be due to the care with which civilised communities interfere to prevent the elimination of idiot infants by the summary process of destroying them. The writer from whom I have just quoted refers to the fact that, even under the Roman Empire, as during the Republic, idiots were looked upon as 'useless entities by the practical Roman.' They had no sanctity in his eyes, and hence their probable rarity; doubtless the unfortunate children were neglected, and there is much reason for believing that they were 'exposed.' 'A congenital idiot soon begins to give trouble,' proceeds Dr. Duncan, 'and to excite unusual attention; and, moreover, unless extra care is given to it, death is sure to ensue in early childhood.' May not idiot children in savage communities have an even worse chance of survival than under the Roman Empire? and may not dolts, boobies, and stupids, _et hoc genus omne_, among savages, have such inferior chances in the infantine and later in the adult struggle for existence, that we may explain thus the comparative rarity of these varieties in savage communities? It certainly does not seem to have been proved as yet that civilisation _per se_ is favourable to the development of insanity.