The growth of rats and mice vibrissae under normal and some abnormal conditions.

The growth of hair from the mystacial vibrissal follicles of C3H mice and Wistar rats has been measured for up to seven cycles. Normally growth in length and thickness was regular and little affected by age or sex. Plucking vibrissae at any stage during the growing period was followed by the appearance of a new vibrissa 8-11 days later. Plucking when growth had ceased had no effect on the time of appearance of the subsequent cycle. New whiskers emerging after plucking grew at the normal rate. Withholding food slowed the growth of vibrissae within 1 day. Normal growth was re-established 3 days after return to full diet.