THEORETICAL CONSIDERATIONS 273 



voluminous to be reviewed here. Vassali-Eandi/^ in 1804, was 

 probably the first to detect evidence of such currents, and stated that 

 the so-called "vital principle" was only "galvanic fluid." Half a cen- 

 tury later A. C. Becquerel ^^'^'^ and Wartmann^'' clearly demonstrated 

 that such currents exist in plants, and several years afterwards the 

 phenomenon was quantitatively studied by Burdon-Sanderson,^^'^^ 

 and Munk.*"' These currents doubtless have their source in the 

 chemical changes going on within the tissues,* and Pfeffer | states, 

 not only that respiratory metabolism {athmungsstoff'wechseT) contrib- 

 utes in an important manner to their formation, but that at present we 

 have no clear proof that they originate otherwise. ^ Also, as Pfeffer 

 says, it is unknown whether the electricity is merely a necessary by- 

 product of chemical transformations that have taken place, or whether 

 it plays a special role in the organism, affecting chemical or other 

 processes. 



The role of these currents is too little understood to make profit- 

 able any attempt to discuss them further as a factor in the response 

 of plants to radium rays, but, since the particles of the beta and alpha 

 rays carry charges of electricity, we should not fail to recognize the 

 fact that the normal electric currents in plants may be a factor in- 

 volved in the reactions of the plants to the stimulus of the rays. Their 

 effect must be either explained or explained away. 



Conclusion : § This rather involved consideration of the possi- 

 ble mode of action of radium rays upon the life-processes of plants 

 has served chiefly to indicate the nature of the problem, and to sug- 

 gest the direction that future researches should take. If the living 

 matter itself is directly affected by the rays it is difficult to conceive 

 how any one function could be modified without the others being 

 affected, for, with long periods of exposure (24 hours or more) to 

 radium of high activity (1,500,000 x or more) it is certain that the 

 protoplasm will have its vitality partially or wholly destroyed, and 

 all " vital " processes correspondingly modified or stopped. But, on 



* Becquerel.^^ 



t6i, p. 192. 



% Gibson's hypothesis that these currents result from the transformation of the 

 energy of light-waves by chlorophyll is referred to on page 261. If his photoelectric 

 hypothesis of photosynthesis shall be confirmed, then it is possible that radium rays 

 may affect photosynthesis, in part at least, by exerting an influence on these currents. 



\ Theoretical considerations with reference to tropistic response, histological 

 effects, and the effects of exposing germ-cells are discussed in Chapters XV, XVI, and 

 XVIII, and are therefore omitted from this chapter. 



