1070 BIOLOGICAL EFFECTS OF RADIATION 



X-rays. — The yeast plant has been exposed to X-rays both before and 

 during the process of fermentation and with results which seem to depend 

 upon just this factor of time of exposure. These experiments were 

 described in their essentials in the preceding section because the same 

 workers tested both respiration and fermentation with the same appara- 

 tus. Since the reports were published in the same year, they appear to be 

 independent and mutually supported, although differing somewhat in 

 the details of procedure. 



Wels and Osann (23) decided that fermentation itself is unaffected, 

 even by strong doses of X-rays, although both growth and reproduction 

 of the yeast is retarded. The CO2 production was measured with a 

 Barcroft manometer and suitable precautions appear to have been taken 

 for such important items as temperature control and the technique of 

 handling the X-rays. These experiments had the characteristic, how- 

 ever, of measurement of CO2 a few hours after the period of exposure. 



The importance of this point appeared in the work of Schneider (19) 

 who reported a 10 per cent reduction in fermentation when the X-rays 

 were being applied. The curve of CO2 production of unradiated yeast 

 coincided with that of yeast exposed some time before measurement, a 

 result in harmony with that of Wels and Osann. Schneider further 

 studied the action of the X-rays by tests to determine other factors which 

 might influence the effect. He found that an important factor was the 

 medium surrounding the yeast cells. The depression in fermentation 

 appeared only in the presence of electrolytes such as NaCl and MgCl2. 



Again we are forced to draw conclusions of a relationship between a 

 process and a form of radiation on the basis of a single set of unconfirmed 

 experiments. The point is clearly in need of more study, but provi- 

 sionally we may assume a small reduction in rate of alcoholic fermenta- 

 tion during exposure to X-rays. 



Heat Effects. — The application of heat to a fermentation mixture has 

 two distinct effects — that of increasing the number of yeast cells and 

 the separate effect on the actual rate of fermentation. To measure 

 or study the latter alone it is necessary to use a short experiment with 

 a relatively large amount of yeast and sugar solution. Of course, the 

 effect is the same in any experiment, but this is the only practical method 

 of avoiding large errors due to the presence of greater numbers of yeast 

 cells. 



When these precautions have been taken, we find that rise in tempera- 

 ture has the same effects that it does on most biological processes with a 

 predominant chemical basis. There is a certain range of temperature 

 throughout which fermentation will take place, an optimum tempera- 

 ture and an effect on the rate of fermentation which is stated by some 

 form of temperature coefficient. In any experiment with fermentation 

 and radiant energy they must be considered, although the use of a con- 



