Drparfrneiit of G o i e f t c s , S t o w s AUriculturcal Expri.inient Stntion, Connecticut
FOUR FIRUHES
I n view of tlie observation by Sturkie ('43) that low temperature may suppress the expression of polydactylism iii fowl, it seemed desirable to test wlicther inhibition of the development of the limb anlage by chemical means has any effect on the polj-dactplous extremity. The earliest expression of polpdactylisni in development is the appearance of a region of rapidly proliferating cells on the preaxial side of the limb. The attempt was therefore made to inhibit the progress of cell-division in the early limb anlage by the use of colchicine, and to depress cellular activity in this region by the use of potassium cyanide and ethyl urethane.
Polydactylisiii in fowls has a variable phenotypic expression, imiging from tlie production of a three-jointed hallux to R seven-toed foot, and the character may be expressed either unilaterally or bilaterally. It was plain, therefore, that a n unequivocal interpretation of experimental results could only he obtained by treatiiient of the enibi-yo in controlled regions and for controlled tinie periods. Accordingly, a method of implanting drug-soaked agar rectangles was employed, by which selected portioiis of tlie embryo could be treated. This method seemed also to afford a iiieans of testing the hypothesis that the gene for polpdactylism iiirolves not only the hallux, hut that it causes a cluplication of the entire limb field. ' S o w a t Department of Biology, Brooklyn College, Brooklyn, N. Y .