J Exp Med. 1925;42:517

THE PRODUCTION OF PERSISTENT ALOPECIA IN RABBITS BY X-RAYS OF VARIOUS DEGREES OF HARDNESS.
Clark H, Sturm E.

1. The minimum dose of x-ray, of each of three degrees of hardness, required to produce persistent alopecia (hair loss) of the abdominal skin of normal white rabbits has been studied. 40 kilovolt rays filtered by 0.5 mm., 50 kilovolt rays filtered by 1 mm., and 70 kilovolt rays filtered by 1.5 mm. of aluminium were employed….snip…3. The values of the critical minimum doses expressed in terms of air ionization (pair of ions per gm. of air divided by 10(15)), for rays produced at 30, 40, 50, and 70 kilovolt peak, are 2.04, 3.7, 4.5, and over 5.1 respectively. The 30 kilovolt value is taken from a previous paper. 4. It is shown that the hair loss reaction deos not parallel to the erythema and pigmentation reactions.