The Specificity of the hair papilla in the rat

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Abstract
A flap of skin on the dorsum of Long‐Evans rats under anesthesia was turned back, the panniculus was excised and hair bulbs in the growing stage with the enclosed papillae were removed with scissors from a 0.5 cm square area. The flap was returned to its original position and the cut edges were sutured. Depapillated areas were biopsied at intervals following the operation, fixed in acetone and histologically prepared to study the distribution of alkaline phosphatase, glycogen changes, growth and differentiation.The hair recedes soon after the operation and is surrounded by the outer sheath cells, some of which remain below the receding hair as an epithelial strand. The latter begins growth and elongation 5–6 days after the operation. Differentiation follows and a fragile hair is formed, but the bulbs seldom have a papilla.The connective tissue in the subcutaneous area apparently cannot be stimulated or does not have the potentiality to become a papilla. Since only a fragile hair is produced by the depapillated follicle, the papilla is very important for the growth of the hair. These observations indicate that the papilla is endowed with special potentialities or has a specificity.