. Evolution and disease . vable that the contact of fish-bones and scales wouldact as irritants and induce a crop of hairs which, beingadvantageous to the bird, have been inherited. It in noway invalidates the argument by urging that skin, notmucous membrane, is furnished with hairs. Even thecomplex intestinal mucous membrane may, under ex-ceptional circumstances, become converted into piloseskin. Such abnormal skin is more likely to possess hairif it be irritated. Abnormal growth of hair from irrita-tion is paralleled by the elongation of the cutaneouspapilla; under similar circumstances. Thi
. Evolution and disease . vable that the contact of fish-bones and scales wouldact as irritants and induce a crop of hairs which, beingadvantageous to the bird, have been inherited. It in noway invalidates the argument by urging that skin, notmucous membrane, is furnished with hairs. Even thecomplex intestinal mucous membrane may, under ex-ceptional circumstances, become converted into piloseskin. Such abnormal skin is more likely to possess hairif it be irritated. Abnormal growth of hair from irrita-tion is paralleled by the elongation of the cutaneouspapilla; under similar circumstances. This may be studied Zeitschrift fiir Physiologic, Bd. iv. p. 121. - Proceedings of the Zoological Society, 1876, p. 335. ENLARGEMENT OF PARTS FROM USE. 27 in lambs. In Britain sheep and lambs are often turnedout to feed on clover grown in fields with the stubblefrom a previous crop of wheat remaining ; the short,stiff, hard ends of the straw irritate the mouth and noseas well as the tender part of the feet above the coronet,. Fig. 15.—The stomach of the Darter {Ilotiis iiiihi>iga), showingthe hairy pyloric plug (Mus. Royal College of Surgeons). and produce a crop of warts. The relation of suchirritation to warts is demonstrated by the fact that whenthe lambs arc removed from the stubble the warts dis-appear. Similar warts gtow on the hands of children 28 EVOLUTION AND DISEASE. when not kept clean; grubbing about in dirt andmuddy, stagnant pools incidental to farmyards willproduce warts on the noses of lambs. The hairless pads on the feet of carnivorous mammalsare made up of closely packed enlarged papilla;. Whenconfined in cages and not kept scrupulously clean, thecombined effects of dirt and limited use often inducesa growth of warts. Sometimes, especially in the coati-mundi, the whole of the pad will be covered withelongated papillae, the appearance of such feet remindingus of the pad on the plantar aspect of the ostrichs toes. The way in which skin responds to external sti
Size: 1449px × 1724px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectabnormalitieshuman
