him that the garden gate of his neighbour has been opened to let out a carriage which he must avoid. A particular smell lets him recognise the place where he is, as stable or kitchen. From the present point of view, it is not exactly the acuteness of the senses which is most important. The acuteness might be equal in a blind person and in a normal person. It might even be greater in the latter, and yet it is only the blind person who can decipher without difficulty raised points so as to understand their meaning as well as when a normal person reads a printed book. This power of the blind person is developed only after a long period of learning, and depends on the appreciation of very delicate tactile impressions. I must point out, moreover, that the method of deciding by means of a pair of compasses gives information only with regard to one side of the tactile sense. However, although we admit that blind people do not really gain anything in the four remaining senses, there is developed in them a special kind of sensibility, which is spoken of in their case as a sixth sense, the “sense of obstacles.” Blind people, especially those who have lost their sight in youth, acquire a surprising habit of avoiding obstacles and of recognising at a distance objects round about them. Blind children, for instance, can play in a garden, without knocking themselves against the trees. Dr. Javal[188] states that some blind people, when passing in front of a house, can count the ground floor windows. A professor, who had been blind from the age of four years, could walk in the garden without striking against a tree or post. He appreciated a wall at a distance of two metres from it. One day, going for the first time into a large apartment, he recognised the presence of a big piece of furniture in the middle, which he took to be a billiard table. Another blind man, walking in the street, could distinguish houses from shops and could count the number of doors and windows. The existence of this sense of obstacles rests upon so many exact facts that it is indubitable. The opinions as to the mechanism by which it operates, however, are very varied. Dr. Zell[189] thinks that it is not a sense peculiar to blind people and “that those of normal sight could equally well acquire it by practice, because it exists in nearly everyone without being noticed.” None the less, there are some blind people who, even in the course of years, do not acquire it. M. Javal, for instance, learnt to read with his fingers extremely well, but was never able to distinguish obstacles at a distance. The most probable hypothesis refers this sixth sense to the action of the tympanic membrane and the auditory apparatus. It is known that loud noise makes it more difficult to perceive obstacles, and snow, by dulling the sound of steps, has a precisely similar effect. Blind tuners, in whom the sense of hearing is well developed, have the sixth sense very marked.