It is possible that slight differences may exist in the seeing powers of different nations, due to the effect of physical conditions: thus, the inhabitants of mountainous districts and of dry elevated tablelands may have a better sight than dwellers in low, humid and level regions, although just the reverse may be the case. Among European nations the Germans are generally supposed to have weak eyes, owing, some imagine, to their excessive indulgence in tobacco, while others attribute the supposed decay to the form of type used in their books, which requires closer looking at than ours in reading. That they will deteriorate still further in this direction, and from being a spectacled people become a blind one, to the joy of their enemies, is not likely to happen, and probably the decadence has been a great deal exaggerated. Animals living in darkness become near-sighted, and then nearer-sighted still and so on progressively until the vanishing point is reached. In a community or nation a similar decline might begin from much reading of German books, or perpetual smoking of pipes with big china bowls, or from some other unknown cause; but the decay could not progress far, because there is nothing in man to take the place of sight, as there is in the blind cave rats and fishes and insects. And if we could survey mankind from China to Peru with all the scientific appliances which are brought to bear on the Board-school children in London and on the nation generally, the differences in the powers of vision in the various races, nations and tribes would probably appear very insignificant. The mistake which eye specialists and writers on the eye make is that they think too much about the eye. When they affirm that the conditions of our civilization are highly injurious to the sight, do they mean all the million conditions or sets of conditions embraced by our system, with the infinite variety of occupations and modes of living which men have, from the lighthouse-keeper to the worker underground, whose day is the dim glimmer of a miner's lamp? "An organ exercised beyond its wont will grow and thus meet increase of demand by increase of supply," Herbert Spencer says; but, he adds, there is a limit soon reached, beyond which it is impossible to go. This increase of demand with us is everywhere--now on this organ and now on that, according to our work and way of life, and the eye is in no worse case than the other organs. There are among us many cases of heart complaint; civilization, in such cases, has put too great a strain on that organ, and it has reached the limit beyond which it cannot go. And so with the eye. The total number of the defective among us is no doubt very large, for we know that our system of life retards--it cannot effectually prevent--the healthy action of natural selection. Nature pulls one way and we pull the other, compassionately trying to save the unfit from the consequences of their unfitness. The