The migration of cells in wool follicles was studied by autoradiography of skin biopsies taken at half-day intervals from 2 to 5 days after intradermal injections of tritiated thymidine in 8 Corriedale sheep on different planes of nutrition. Cell migration rates were not the same in all follicles. Therefore, the shortest and longest times for cells to migrate to defined levels in the follicles were determined. Cells of the inner root sheath moved up the proximal part of some follicles ahead of

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... ontemporaneously formed cells in the fibre. Subsequently, cells in the fibre reached the level where the fibre attained its definitive form in about 2-5-4 days. Cell migration also occurred in the outer root sheath, and sloughing of both outer and inner root sheath cells was observed. In the distal half of the follicles, cells of the root sheaths and of the fibre migrated at similar rates, which suggested that the inner root sheath and fibre were carried through the upper part of the follicle by migrating cells of the outer root sheath. Cell migration times were about 0-5 day less in fat sheep on large and moderate food intakes than in lean sheep on restricted intakes.