r o i ~n Tiniwrmty T W O FIGURES lNTRODUCTIOlN
Enzyme systenis in vivo have long been considered highly resistant tc x-radiation. In particular, the investigations of Wels and Osann ( '25) and of Euler and his co-workers (Euler, hhlstrom and Hogberg, '43) indicated that fairly large doses of x-rays have practically 110 effect in diminishing the activity of the enzymes associated with fermentation and respir a t' ion in microorganisms. Such results are all the more interesting in view of the fact that in some cases only 10% or lcss of tlie irradiated cells are capable of formiiig new colonies (Anderson and Turkowitz, '41 ; Hevesy, '48).
I n the present paper, howe~er, we shall attempt to demonstrate that under certain experinieiital conditions there is a readily detectable effect of x-rays on enzyme activities in zico. Later papers in tlie proposed series 011 yeast cells will deal with other enzyme systems, particularly adaptive enzymes, with further variations in the media, and with variations in dose and dose-rate of the irradiation. A general aini of such We wish to express our deep appreciation to Dr. Emanuel Benjamin, Radiologis4 of Providence, R. I., for the use of his x ray equipment during the course of this investigation.
a P a r t of the work was farilitatrd hy a grant from the American Cancer Socirty recorninended by the Committee 011 Growth of the National Research Council.