400 PROTOPLASMIC ACTION AND NERVOUS ACTION 



growing regions (terminal buds) initiates growth in the 

 dormant regions adjacent (axillary buds, etc.); any 

 arrest of growth by cold, anaesthetization, or removal 

 of oxygen has the same effect.^ Such facts show that 

 pronounced activity of growth-processes in one region in 

 some manner involves repression of similar processes 

 in neighboring regions; and this effect has been shown 

 in certain cases to be independent of the transport of 

 special growth-inhibiting substances between the two 

 regions.^ A similar inhibitory influence of one embryonic 

 area on another is seen also in the development of 

 animals. 3 



The hypothesis that the essential basis of this growth- 

 controlling influence is electrical is consistent with the 

 observation that in certain organisms the rate and direc- 

 tion of grow^th can be experimentally controlled by 

 electric currents. We have seen that in hydroid stems 

 the growing or regenerating hydranths are negative 

 relatively to other regions of the stem and to the stolons. 

 Apparently, therefore, a normal accompaniment of 

 growth is the passage of electric currents in a constant 

 direction through the organism; and the direction of 

 the current through the galvanometer shows that the 

 positive stream enters the living system (from the 

 exterior) at the regions where growth is most rapid. 

 If electric currents are in themselves a factor in the 



^McCallum, "Regeneration in Plants," Bot. Gaz., XL (1905), 97, 

 241. 



2 Child and Bellamy, Science, L (1919), 362; Bot. Gaz., LXX (1920), 

 249; Harvey, America^i Naturalist, LIV (1920), 362. 



3 Cf. Stockard, American Journal of Anatomy, XXVIII (192 1), 

 115- 



