PHYSICO-CHEMICAL BASIS OF TRANSMISSION 401 



growth process, it is to be expected that their passage 

 through the organism from without should either 

 promote or inhibit growth according to the direction of 

 flow. Lund has in fact recently shown that the regenera- 

 tion of new polyps from the cut stems of the hydroid 

 Obelia may be controlled by weak electric currents 

 passed lengthwise through the stems ;^ the formation of 

 hydranths is promoted where the current passes so as 

 to enter the protoplasm from the medium — i.e., at the 

 cut end facing the positive pole of the battery — and 

 inhibited at the other end. The normal polarity of a 

 stem can thus be reversed by passing the current, a 

 result in agreement with the view previously expressed 

 by Mathews that morphological polarity in these 

 organisms has an electrical basis.^ Bose has also found 

 that the electric current influences growth processes in 

 the higher plants in a polar manner, the anode enhancing 

 and the cathode depressing the normal rate.^. Recently 

 Ingvar has reported experiments in which the outgrowth 

 of processes from embryonic nerve cells is influenced in a 

 directive manner by the passage of weak currents 

 through the culture medium. Here also a polar influence 

 is seen, the processes growing toward the anode differing 

 morphologically from those growing toward the cathode.^ 

 All of these facts show clearly that growth processes 

 resemble the processes of stimulation in irritable tissues 

 in being subject to electrical control; further that in this 



^ Lund, Journal of Experimental Zoology, XXXIV (192 1), 47i- 



2 Mathews, loc. cit. 



3 Bose, Proceedings oj the Royal Society, B, XC (19 18), 364. 



4 Ingvar, Proceedings of the Society oJ Experimental Biology and 

 Medicine, XVII (1920), 198. 



