Abstract
1. Effects of starvation or treatment with a cation exchange resin, dowex 50, parallel in some respects those seen earlier on the respiration and fermentation of bakers' yeast receiving 90,000 r of 250 kv. x-rays. Starvation increased the radiosensitivity of cell division processes whether measured by colony formation or by turbidimetric determination of growth in a liquid medium. The dowex 50 enhanced the radiation effect by the latter measure but appeared to increase colony formation of irradiated yeast. 2. The effects on growth differ from those on respiration and fermentation in that the exchange resin treatment did not inhibit colony formation further, and neither starvation nor resin appreciably altered the growth of non-irradiated yeast. 3. Two effects of radiation are seen in these experiments: (a) a permanent inhibition of growth, and (b) a temporary inhibition of the remaining cells resulting in delay of growth. 4. The irradiated cell is more dependent on certain aspects of its environment in terms of growth responses as well as in terms of metabolism (i.e. respiration and fermentation). Whether or not potassium plays a role in the growth response as it does in the metabolic response cannot be ascertained from the present data.