Magnetic field dependence of the TBE. The frequency of Tennis Ball Effect (TBE) in two populations of cysteine-dejellied fertilizable Xenopus eggs as a function of field strength, gradient strength, and magnet exposure time. (A) Temporal evolution of TBE II at different field strengths (in T). The diagram only gives field exposure times. The total duration of the experiment was about 50 min longer. Each individual point in the diagrams represents a group of about 150 cells. The standard deviation in TBE count, as determined from the four Petri dishes positioned at 9.4 T field strength in the center of the magnet, was 12.3 %. A total of about five percent of the eggs obtained from one ovulation were nekrotic. These were not considered when calculating TBE percentages. (B) TBE percentages after 109 min of continuous magnetic field exposure as a function of field strength and field gradient strength. The TBE counts were all performed after fixation of the eggs, and the standard deviation in the four central dishes was 0.7 % for TBE I and 1.2 % for TBE II. IMM = percentage of immature oocytes present in the dish.