“An inverted principle. The brain can think for itself. The eye can only complain, and not always very clearly in the case of a child. Moreover, Mrs. Sharpless, in your school-days the eye wasn’t under half the strain that it is in our modern, print-crowded world. The fact is, we’ve made a tremendous leap forward, and radically changed a habit and practice built up through hundreds and thousands of years, and Nature is struggling against great difficulties to catch up with us.”
“I don’t understand what you are getting at,” said Mrs. Clyde, letting her magazine drop.
“Have you tried walking on all fours lately?” inquired the physician.
“Not for a number of years.”
“Presumably you would find it awkward. Yet if, through some pressure of necessity, the human race should have to return to the quadrupedal method, the alteration in life would be less radical than we have imposed upon our vision in the last few generations.”
“Sounds like flat nonsense to me,” said the downright Clyde. “We see just as all our ancestors saw.”
“Think again. Our ancestors, back a very few generations, were an outdoor race living in a world of wide horizons. Their eyes could range over far distances, unchecked, instead of being hemmed in most of the time by four walls. They were farsighted. Indeed, their survival depended upon their being far-sighted; like the animals which they killed or which killed them, according as the human or the beast had the best eyes. Nowadays, in order to live we must read and write. That is, the primal demand upon the eye is that it shall see keenly near at hand instead of far off. The whole hereditary training of the organ has been inverted, as if a mountaineer should be set to diving for pearls; and the poor thing hasn’t had time to adjust itself yet. We employ our vision for close work ten times as much as we did a hundred years ago and ten thousand times as much as we did ten thousand years ago. But the influence of those ten thousand years is still strong upon us, and the human child is born with the eye of a savage or an animal.”
“What kind of an animal’s eyes have I got?” demanded Bettina. “A antelope’s?”
“Almost as far-sighted,” returned the Health Master, wriggling out from under her and catching her expertly as she fell. “And how do you think an antelope would be doing fine needlework in a kindergarten?”
“But, Strong, few of us go blind,” said Mr. Clyde. “And of those who do, nearly half are needlessly so. That we aren’t all groping, sightless, about the earth is due to the marvelous adaptability of our eyes. And it is exactly upon that adaptability that we are so prone to impose; working a willing horse to death. In the young the muscles of accommodation, whereby the vision is focused, are almost incredibly powerful; far more so than in the adult. The Cherub, here, could force her vision to almost any kind of work and the eye would not complain much—at this time. But later on the effects would be manifest. Therefore we have to watch the eye very closely until it begins to grow old, which is at about twelve years or so. In the adult the eye very readily lets its owner know if anything is wrong. Only fools disregard that warning. But in the developing years we must see to it that those muscles, set to the task of overcoming generations of custom, do not overwork and upset the whole nervous organization. Sometimes glasses are necessary; usually, only care.”