RADIATION AND RESPIRATION 1063 



radiation does influence respiration. However, this reported increase 

 agrees with the effect of ultra-violet on alcoholic fermentation which is 

 often pronounced in pea seeds, especially during the early stages of 

 germination when there is a shortage of O2 within the seed coats. 



X-rays. — The group of waves known as roentgen or X-rays have been 

 tested rather carefully on two types of plants for their effect on respira- 

 tion but the results are in part contradictory. They indicate either 

 no influence with nondestructive doses or a depression of the respiratory 

 intensity, especially with doses which are so injurious as to prevent 

 continued growth of the plants involved. 



The work which points to no effect on respiration, even though 

 growth and reproduction are severely retarded at the same time, was 

 reported by Wels and Osann (23) in 1925, though the senior author had 

 reported like results from a few experiments in the preceding year. 

 The plant used for the main report was yeast and the respiration was 

 measured by the O2 consumption in a Barcroft manometer a few hours 

 after irradiation. The experimental technique for handling the X-rays 

 and attention to such details as proper temperature control of the 

 irradiated yeast suspension appear to warrant confidence in the data 

 obtained. Even though the periods of exposure to the rays were from 



2 to 8 hr. with such a strength of radiation that 1 hr. was equivalent 

 to 12 units of the human erythema dose (denoted as H.E.D.), there was 

 no change in the rate of oxygen consumption, at least when it was 

 measured. At the same time, the rate of increase of yeast cells decreased 

 in proportion to the length of the exposure. 



This positive effect indicates that the X-rays were actually absorbed 

 by the yeast cells. Likewise the absence of change in the rate of fermen- 

 tation (see next section of this paper) under the same conditions suggests 

 that the oxygen consumption is a fair measure of the respiration in these 

 cells because of the close relationship between alcoholic fermentation 

 and normal plant respiration. However, Schneider (19) reported a 

 10 per cent decrease in fermentation by yeast exposed to a dose of 



3 H.E.D. during the actual process, so that an element of uncertainty 

 is present even in these otherwise conclusive results. The critical 

 test would be to measure the O2 consumption under conditions unfavor- 

 able to fermentation and at the same time expose the yeast to X-rays. 

 This has not been done. 



The retardation of respiration by X-rays has been demonstrated in 

 seeds and seedlings by two workers, Bersa (1) in Austria and Miss John- 

 son (6) in the United States. The latter reported only a depression but 

 she used strong doses for a "few" hours. Bersa found a brief, slight 

 acceleration with much weaker doses, but after 2 or 3 days the rate of 

 respiration had fallen to about 57 per cent of the normal. Both workers 

 exposed moist seeds and measured the results in the growing seedlings, 



