From the results of his numerous plant and animal experiments, Hammett arrived at the conclusion that the sulphydryl radicle, naturally present in all cells, was the essential and universal stimulus to growth by increase in the number of cells. This hypothesis did not long remain unchallenged. Others, after carrying out similar investigations, have either not been able to reproduce Hammett's results, or have preferred to lend to them another interpretation. Reimann translated Hammett's work into the clinic and reported instances of chronic indolent ulcers which healed with dramatic swiftness following the direct application of sulphydryl compounds. He described a rapid proliferation of both the fibroblastic and epithelial elements of the wound. In recent years Rose has demonstrated methionine and not cystine to be the indispensable sulphur-containing amino-acid. Cystine stimulated growth only in the presence of methionine. In the absence of the latter from the ration, however, the animals rapidly lost weight and died, even though an abundant amount of cystine had been supplied. The purpose of these experiments was to determine whether a deprivation of cystine and methionine in a degree sufficient to abruptly arrest growth, had any effect on the healing of soft tissue wounds. The tensile strength of the wound was used as an index of healing. Young growing rats weighing between 90 and 100 g were divided into 2 groups: (1) normal control, (2) sulphur-ammo-acid deficient. The experimental diet used was that described by Dyer and du Vigneaud, and consisted of: This is a full diet, adequate in all the essential constituents except the sulphur-bearing amino-acids. It contains cystine and methionine sufficient only for the maintenance of the animal but not for normal growth and increase in weight.