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.
The examples I have given show that the human body possesses senses which come into operation only in special conditions, and which require a special education. The “sense of life” to a certain extent comes within this category. In some persons it develops very imperfectly, generally revealing itself only late in life, but sometimes a disease or the danger of losing life stimulates its earlier development. Occasionally in persons who have tried to commit suicide, a strong instinct of life wakens suddenly, and impels them to make frantic efforts to escape.
It happens, therefore, that the sense of life develops sometimes in healthy people, sometimes in those who suffer from acute or chronic disease. These variations are parallel with the development of the sexual instinct, which in some women is completely absent and in others develops only very late. In certain cases, it is awakened only by special conditions, such as child-birth, or even some defect of health.
As the sense of life can be developed, special pains ought to be taken with it, just as with the making perfect of the other senses in the blind. Young people who are inclined to pessimism ought to be informed that their condition of mind is only temporary, and that according to the laws of human nature it will later on be replaced by optimism.