270 THEORETICAL CONSIDERATIONS 



the conductivity of solutions of radium bromide of 1/12,000 to 1/20 N 

 concentration was similar to that of analogous, but non-radioactive, 

 salts of elements related to radium, c. g., barium, strontium, and cal- 

 cium, and in 1906 Kohlrausch'^^ definitely stated that the conductivity 

 of water is not increased by drawing through it a current of air that 

 has first passed over radium. The quantity of ions thus formed, he 

 said, is exceedingly small. Experimenting with NaCl, CaCl, BaCl, 

 MgSO,, ZnSO,, K2CO3, HCl, and NaOH, in percentages of from 20 

 to 2.5, he found that radium rays increase the conductivity of elec- 

 trolytes only in so far as they raise the temperature of the solution. 

 He inferred that, if the /9 and y rays do increase the degree of ioni- 

 zation of the electrolyte, they do so to a degree too small to be de- 

 tected by the delicate means he employed.* 



Growth: As previously stated,! the term growth is here taken 

 to mean increase in size or increase in mass, one or both, with or 

 without an accompanying change of form. Increase of size with- 

 out increase of dry weight involves increased turgor in elastic walled 

 cells. Increase of mass involves an excess of constructive over de- 

 structive metabolism. Radium rays may affect both processes. 



Since turgor is an expression of the internal osmotic pressure of 

 the cell, and since osmotic pressure is a function of the number of 

 particles of the solutes present in the cell-sap, radium rays, by their 

 power of ionization, may possibly increase this turgor, and thus accel- 

 erate or favor an increase of size of the individual cells and of the 

 tissues and organs composed of them. Theoretically the rays would 

 have this power. That they do alter solutions in some manner seems 

 clearly evident from the effects of exposed water on germination and 

 growth, as described in Experiments 48-51 on pages 158-173. 



Growth, in the sense of increase of mass, is an expression of con- 

 strutive metabolism. Not only is the number of biogen molecules 

 increased, but also the amounts of various substances produced by 

 them. Here, as in respiration, fermentation, and other metabolic 

 processes, the activity of enzymes is involved. The digestion of the 

 food is accomplished by various enzymes, and energy for metabolism 

 is set free by enzymotic action. Verworn % believes that a molecule 

 of an enzyme is the substratum of the metabolic process. It is the 



* Cf . foot-note, pp. 220-221. 

 tp. 223. 

 t2, p. 15. 



