Cannefax, George R. (Communicable Disease Center, Atlanta, Ga.). A temperature-gradient bar and its applications to the study of temperature effects on the growth of Reiter's treponeme. J. Bacteriol. 83:708–710. 1962.—A temperature-gradient device is described which employs a constant heat source and an aluminum bar with 294 holes to accommodate small test tubes. Examples of the range and degree of temperature gradients are presented, and the factors affecting heat conduction and heat losses are discussed. Three temperature gradients obtained under different conditions are shown graphically. The usefulness of the temperature-gradient bar in determining the optimal temperature for the cultivation of Reiter's treponeme is presented. The optimal temperature range was found to be 33 to 35 C. The potential usefulness of the temperature-gradient bar in other biological studies is suggested.