Carcinogen label-retaining cells in the hair follicle. Eight-week-old mice were treated with a single topical application of [3H]DMBA. Seven weeks later, samples of the dorsal skin were fixed, and cross sections were prepared. Note the carcinogen-retaining cell in the middle third of the follicle (arrowhead). e, epidermis; d, dermis; h, hair follicle; a, arrector pilorum muscle. Original magnification, ×630.