It is generally agreed that proliferating cells show greater susceptibility to the effects of ioiiiziiig raps than resting cells (Carson, '42 ; Holthuscii, '21 ; Langcndorff, '31 ; Marshak, '35 ; Newcornbe, '42 ; Sax aiid Swaiisoii, '41 ; Strangeways and Hopwood, '26 ; and Vintembcrger, '28). In order to study the quantitative effects of x-rays cytologically and physiologically it became desirable to obtain material in whicli all the cells arc in the same mitotic stage. The difficulty of obtaining such inaterial suggested the use of diapause eggs of grasshoppers where every cell is in the resting condition and remains in that state uiitil cold-treated to induce further development (Tahmisian, unpublished ; Bodine, '29 ; and Slifer, ' 3 2 ) . Cell division does not occur in the diapause enibryo. The inaterial is cytologically, physiologicallp, and morphologically basal in metabolic activity.
Grasshopper eggs are excellent test objects to use for a study of the effects of x-rays on respiration. Each egg may be used as a unit, and the oxygen uptake may be measured on individual eggs with a Cartesian Diver Microrespirometer. If more than one egg is used, any alteration from the control can be explained by the average group effect. Should there be a n inhibition in respiration, the diminution could mean a destruction of enzymes or substrates due to irradiation effects in every unit, or a change due to the fact that the per-