In a previous paper (Spear and Glücksmann, 1938) the effect of a single γ-ray exposure on the tissues of the normal tadpole were described. It was shown that radiation had a special effect upon cells in the “mitotic areas,” and quantitative results were given of the changes observed in the brain and eye of exposed animals. These indicated that radiation caused a diminution in cell division, followed by the appearance of degeneration (Fig. 1). The sequence of events was explained as an effect of radiation upon potential dividing cells, unfitting many of them for the ordeal of mitosis, and leading to their breakdown.

To determine more precisely the relation between disturbance of cell division and the occurrence of degeneration, some preliminary attempts were made to vary the mitotic activity in unirradiated tadpoles: (a) by fasting, and (b) by low temperature. It was found that animals could survive in tap water without food for more than three weeks, and that during this period they showed a steady diminution in cell division, which eventually reached zero.

It was also found that tadpoles could live for some time at temperatures as low as 0·5°C. to 0·3°C. Under such conditions proliferative activity was considerably modified; there were fewer cells in prophase, and the actual process of mitosis, especially the metaphase, was prolonged.