THE HEREDITARY TRANSMISSION OF PHYSICAL DEFECTS.
[TO THE EDITOR OF THE "SPECTATOR")
Sin,—In the Spectator of the 16th ult. you express a doubt whether short-sight tends to become hereditary, and give as one of your reasons that " the Chinese habit of spoiling the foot has not injured the feet of any new-born baby." I do not know whether we have information enough on the subject to be certais of this, but if it is true, I fear we cannot reason from this to the• case of short-sight. After carefully reading Darwin's work on "The Variation of Animals and Plants under Domestication,"
the conclusion from his facts respecting the hereditary transmis- sion of acquired characters appears to be that they are much more liable to be transmitted when functionally produced than when produced by externally acting causes. The Chinese practice of crippling the feet is an externally acting cause. Short-sight, on the contrary, when not congenital, is a functionally produced -character, due to the effort of the eye to accommodate itself to short distances. I have little doubt that a common cause, per- haps the commonest, of short-sight is bad print, which compels the reader to hold the book too near his eyes. And this cause is very much within the power of public authorities to control, by requiring school books to be in sufficiently large type. But light is probably another prevailing cause, and this also admits of con- trol and remedy, by every one who has the responsibility of providing light for study or work.—I am, Sir, &c.,
JOSEPH JOHS MURPHY.
Old Forge, Dunmurry, County Antrim, February 25.
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