906 BIOLOGICAL EFFECTS OF RADIATION 



the cell to become old prematurely. This last statement is in accord with 

 evidence obtained from the higher plants, but as for the fungi there is 

 some question as to whether a stimulation of total growth can be obtained 

 with X-rays. 



The metabolic state of the cell, its reproductive activity, as well 

 as the composition of the surrounding medium, all affect the sensitivity 

 of the cell to X-rays. Lacassagne and Holweck (97) reported that 

 yeast cells in a quiescent state are more sensitive to X-rays than actively 

 dividing cells. This is in accord with the generally accepted theory that 

 quiescent cells in general are more sensitive to radiation than cells in 

 division. Schneider (165) found that yeast cells which are causing active 

 fermentation in a sugar solution are much more sensitive to X-rays than 

 those which are irradiated dry. A number of investigators have reported 

 that the sensitivity of the fungus cell is increased markedly by the 

 addition of an electrolyte to the medium. Schneider (165), Groedel 

 and Schneider (60), and Zeller (197) have noted the sensitizing action 

 of a number of different salts. Pichler and Wober (146) reported that 

 the action of X-rays on spores of Ustilago Tritici and Chrysophlyctis 

 endohioticum is greatly increased if the spores are irradiated in an acid 

 medium, especially in the presence of oxygen or of oxygen-yielding 

 compounds. Increased sensitivity produced by a change in medium 

 has been interpreted as due to the production of harmful ions by radiation 

 or as due to increased permeability of the fungus cell as a result of irradia- 

 tion. Both of these factors are probably involved, but at the present 

 time there is little more that can be said about the nature of the sensitiza- 

 tion. Some salts may decrease instead of increase sensitization. The 

 antagonistic action of potassium chloride to the aging effects of X-rays 

 is exceedingly interesting from both a theoretical and a practical point of 

 view. It was observed by Nadson and Zolkevifi (136) that the harmful 

 influences of X-rays on yeast may be entirely eliminated if 0.5 to 1.5 per 

 cent potassium chloride is added to the substrate. They found that the 

 antagonism is dependent on a definite ratio between the amount of 

 potassium and the intensity of X-rays. Sodium chloride does not exert 

 such a balancing effect. 



Saltation is another interesting effect produced by X-rays. Nadson 

 and Philippov (133) and Dickson (29, 30) reported saltants produced 

 in this way. The characters of some of the saltants remained constant 

 through a number of succeeding generations. Nadson and Philippov 

 used Mucor and Dickson used Phycomyces Blakesleanus and several 

 species of Chaetomium. Dickson found that different species in the same 

 genus vary markedly in their ability to saltate when exposed to X-rays. 

 He also reported that old cultures saltate much more readily than younger 

 ones. Little correlation was found between the normal variability of 

 the fungus and its capacity to produce saltants with X-rays. 



