Visual Education (Jan-Nov 1920)

32 Visual Education sensitive olfactory nerves. It is the same with domestic animals. The ears of a horse or a dog, rather than his eyes, express his emotions. One might suspect by analogy with the foregoing facts that the most civilized races of men have the best eyes. Such appears to be the case, though the evidence is not conclusive. The writer has tested the ability of Indians and low-caste Mexicans both to see very faint objects and also to see as separate points two objects which were apparently very close together. Most of these tests were on the stars. He has also tested many white people. The Indians and Mexicans had whatever advantage there may have been because of some familiarity with the objects, for they are much better acquainted with the stars than most white people are. Nevertheless, it was found that not only were their best eyes inferior in both respects to the best eyes of white people, but also their eyes averaged much less nearly perfect. The name given by the keen-eyed Arabs to the little star near the larger one at the bend of the handle of the Big Dipper, was Alcor (the test), although it is easily seen by anyone whose eyes are anywhere nearly normal ; and although these Arabs were for some centuries the leading astronomers of the world and made extensive catalogs of the stars, they failed to see a number of objects that are visible to half of present-day university students. Partisans of Visual Education might suggest that the most intelligent species of animals owe their intellectual position to their superior powers of sight. Is it not probable, rather, that in a general way the evolutions of the central nervous system and the various sense organs have kept pace with each other, and that one sense or another has become most highly developed in a species according to its environment and the demands of its life ? We are probably correct in picturing to ourselves the remote ancestors of the present highest forms of life as lowly creatures, living in the slime of far-off geologic ages. Day after day, with rhythmic periodicity, the sun stimulated their rudimentary eye-specks, and through them their central nervous systems. The ebb and flow of tides and the daily variations in temperature also prevented their life processes from descending to a dull uniformity. As a consequence of the stimuli from without and the inherent potentialities of the matter of which they were composed, they developed through millions of years into the forms that exist on the earth today. The senses of animals of all types more or less perfectly meet their needs. Kudimentary eyes are sufficient for the lower forms. In caves certain Araclmidae, and, in both caves and the deep sea, even fishes have either no eyes at all or only useless ones. The eyes of fishes in shallow water have lenses of a convexity exactly adapted to such a medium. The pupils of the eyes of herbivorous animals are elongated horizontally, and a result of this is that they can focus most sharply on vertical lines such as grasses present. On the other hand, the pupils of the eyes of cats and other carnivorous animals are longest in the vertical direction, and a result of this is that they can focus most sharply on things darting to the right or left. Man needs better eyes than other animals to meet the requirements of his life, and he has them. The demands have enormously increased in the last few generations, particularly because of the developments in printing, strong artificial lights, and rapid locomotion. Apparently our eyes are meeting