Critical maximum temperatures EL Karlstam 1954 Buffo bovera and Buffo canorus Oct. 4 see R.C. Steblin's field notebook July 3, 1951 for description of apparatus and technique. This set-up used by Vanderickson, Steblins, Rosenthal with but slight modifications. I used 4" peanut butter jars to house the animals, 4 thicknesses of saturated paper towel, and a larger 5 mm. glass "breathing tube". The water stirrer I used was a Fisher propeller-type (60 cycle) one. 3 0-50°c rapid recording thermometers were used, all agreeing within 0.1°c. of each other. One of these was used to check water bath temps in addition to the -20-110°c thermometer changed in position. Hot plate set at "6.5" and warmed prior to placing the water chamber in position. The stirrer was efficient since surface water temps. varied < 0.1°c. any part of bath. However, Jor B3 were lower in position and closer to the hot plate. Following Exp't. #1 I re-calibrated the dualtherm quick recording thermometers. The one in Jor B3 reads 0.3°c. higher than the other two at 20-25° range, but above 40° all three agree. Therefore, I'll leave the recorded temperatures as they now stand.