The effect of a single plucking at different times in the hair cycle on the growth of individual mouse vibrissae

SUMMARY Mouse vibrissae have been plucked at precise times throughout the hair cycle and the time of appearance of the new hair noted for each Individual follicle. It was found that plucking a vibrissa at any time during the cycle resulted in the induction of a new hair and in no case did the follicle continue the same cycle. All the vibrissae grew at the normal rate of 1.0 mm/day for most of the growing period and whenever plucked during this period a new hair appeared after 8–11 days. When the growth rate fell to 0.6–0.7 mm/day at the end of the growing period plucking resulted in the appearance of a new hair after 7 days. When the growth rate fell to 0.1–0.3 mm/day a new hair appeared 5 days after plucking, thus the time of normal eruption was not altered. When whiskers were 10–15 mm long and about half way through the active growth phase their follicles were surgically transected at one of three different levels: (1) just above the dermal papilla which left all or most of the differentiating matrix cells, (2) mid‐follicle and (3) at the level of the sebaceous gland. In each case the distal part of the hair was then plucked. In five out of ten cases when the cut was made just above the dermal papilla a new hair erupted after a variable time 10–15 days. In all other cases the existing hair cycle was completed after a delay of a few days. This emphasizes the importance of the differentiated matrix cells in the maintenance of the hair cycle.