Embryology (1949) Embryology embryology00bart Year: 1949 TRANSPLANTED NORMAL SITE LIMB BUD OF LIMB BUD NORMAL LIMB NERVES 2 6,7,8 NERVES SUPPLY TRANSPLANTED LIMB Fig. 87. The transplanted forelimb fails to direct the third, fourth, and fifth nerves toward itself if it is placed too far away from the origin of these nerves. In the position indicated the limb becomes innervated by the sixth, seventh, and eighth spinal nerves. and when they reach it they turn back and enter the limb. Therefore, there seems to be a general stimulus, a general attraction, exercised by growing organs for nerves.
Embryology (1949) Embryology embryology00bart Year: 1949 TRANSPLANTED NORMAL SITE LIMB BUD OF LIMB BUD NORMAL LIMB NERVES 2 6,7,8 NERVES SUPPLY TRANSPLANTED LIMB Fig. 87. The transplanted forelimb fails to direct the third, fourth, and fifth nerves toward itself if it is placed too far away from the origin of these nerves. In the position indicated the limb becomes innervated by the sixth, seventh, and eighth spinal nerves. and when they reach it they turn back and enter the limb. Therefore, there seems to be a general stimulus, a general attraction, exercised by growing organs for nerves. It does not seem to make any difference whether this general attraction is exercised by the limb or by the nasal placode. The nerve fibers of the limb do not, however, penetrate a foreign object. Thus there is a specificity which determines the penetration of nerve fibers into a tissue, and this is independent of the attractive forces. Theories of control of nerve outgrowths What could be the nature of this general attraction exercised by all growing structures? Three theories or three interpretations have been sug- gested. There may be a chemical attraction exercised by the limb over these growing nerves. Another suggestion is that the directive force is an electrical force. Finally, there may be a mechanical direction of the nerve fiber.
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