. Evolution and disease . thehairs gradually return to their normal condition. Thisovergrowth of hair may be attributed to a local increasein the blood supply, for it is a fundamental principle inPathology that irritation produces redness of the skin ;the heightened colour is a consequence of additionalsupply of blood to the part. Hunter demonstrated therelation between blood supply and overgrowth in an in-genious way: he transferred the spurs of cocks to thevascular tissue of the comb ; here they took root and, inconsequence of the extra supply of blood, and in part nodoubt from disuse, grew
. Evolution and disease . thehairs gradually return to their normal condition. Thisovergrowth of hair may be attributed to a local increasein the blood supply, for it is a fundamental principle inPathology that irritation produces redness of the skin ;the heightened colour is a consequence of additionalsupply of blood to the part. Hunter demonstrated therelation between blood supply and overgrowth in an in-genious way: he transferred the spurs of cocks to thevascular tissue of the comb ; here they took root and, inconsequence of the extra supply of blood, and in part nodoubt from disuse, grew inordinately. These specimens, 22 EVOLUTION AND DISEASE. in company with several others, are preserved in themuseum of the Royal College of Surgeons (fig. n). The additional supply of blood to a part abnormallyfunctional or irritated seems to be largely due to nervousinfluence, as the following experiments show. Bidderexcised a piece of the sympathetic nerve in the neck ofa young growing rabbit. This was followed by over-. Fig. ii.—The head of a cock with its spur transferredto the comb. growth of the ear of the same side. The experimenthas been repeated by Sterling on young and growingrabbits, and on dogs. A piece of the vagus and sym-pathetic—for in dogs both nerves are contained in thesame sheath—was excised. In all cases the ear on thisside became distinctly longer, broader, and somewhatthicker than its fellow. The hair was longer and ENLARGEMENT OF PARTS FROM USE. 23 ;-t*4iiik - stronger on the side operated upon, and the ear remaineddistinctly warmer. The relation of irritation upon nerves in connectionwith overgrowth of dermal structures may be illustratedby the curious defect known as spina bifida occulta. Inthis malformation the bony arches covering the spinalcord are defective, and thenerves issuing from the cordat this spot are involved infibrous tissue or compressedby an accumulation of is no uncommon eventto find the skin covering thedefective parts of
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Keywords: ., bookcentury1800, bookdecade1, booksubjectcongenitalabnormalities
