NINETEEN FIGUBES
JOURKAL OFMOKPROMGY, VOL. 103, NO. 3 NOVEYBER 195.8 BENJAMIN DALE STIXSON tained indicate that both cysteine and cystearnine confer a significant enhancemeiit of radioresistance as measured by the regeiierative and developmeiital capacities of limbs. MATERIALS AND METHODS Larvae of Desnzogwthus f uscus, Amby/atoma opaczini, A. tigrixunz, and A. rnaculafum were obtained from Tennessee. Some eggs of A . opaczim were collected on Long Island, New York. Larvae of Triturzis torosus which had heen collected in California were generously provided by Dr. 11. C. Nui of the Rockefeller Institute for Medical Research. Several species were employed because of the difficulty of maintaining large numbers of the same species over the requisite time interval. Chcwical trectt?izenfPreliminary stuclics of larval tolerance to immersion in cysteine solutions were performed with larvae of A.r?zbysfonzri opacum, measuring 22-24 min in length. Resiilts indicated that such animals tolerate immersion in a coiicentration of 0.1% cysteine for 1-3 hours at room temperatiire. Tests of tolerance to cystanline (disulfide of heta-mercaptoethvlamine) under id(~ntica1 conditions also indicated a coiicentration of 0.170 for this compound. Tlarvae of A . w%crculcitunz of comparable length survired a concentration of 0.087. cystearnine (-SH) for pcriods exceeding one hour. Hence, these mere the coiiccntr a t' ions employed in tests of the possible effects of the varioiis compounds on l a 1~a l radioseiisitivity, regardless of the species used ill it given experiment. A 0.1% solution of rA-cystcine I-ICI (Merck) mas prepared by dissolving 1.0 grri in one liter of 10% Ringer's solution (minus bicarbonate and phosphate) j the solution was then adjusted to pH 7.0 hp the addition of 2 N KaOI'l. Solutions of cystaminc (-SX-) were preparcd in the *Both cystexmine and cystamin? (Reeaptan) TveTe made available for thls study through the courtesy of Dr. Walter G. Christiansen, Associate Director for Labaz Laboratories in the TTnited States.
Stage I. W o u i t d healing and regmssiopz.Btage W . Two-digit stage.Xtage V . Three-digit stage.
