METHODS OF PHYSIOLOGICAL ANALYSIS 79 



Hyman (1918), Hyman and Bellamy (1922), and Child and Hyman (1926) 

 suggested that the axial potential difference observed in many animals 

 originates in metabolic differences. Lund and his co-workers, in various 

 papers from 1926 on, have maintained, as the result of determinations of 

 oxygen consumption and comparative estimations of CO2 production, de- 

 crease of potential difference and of oxygen consumption by cyanide, dif- 

 ferential reduction of methylene blue, and other experiments, that electric 

 polarity is quantitatively correlated with oxidation — in other words, that 

 the axial potential differences are expressions of an axial metabolic gradi- 

 ent. It was further suggested by Child (1924&, chap, xi) that, if the poten- 

 tial differences give rise to currents under natural conditions, such currents 

 may be important factors in physiological dominance and correlation. In 

 his later papers Lund assumes that currents do flow under natural, as well 

 as under experimental, conditions, and emphasizes their importance as 

 factors in correlation. Barth, on the other hand, finds "no coincidence of 

 electric polarity and organic polarity in different hydroids"; that is, in 

 some forms the apical region is galvanometrically positive, in others nega- 

 tive, to lower levels, and in isolated pieces cut ends may be at first nega- 

 tive, later positive, or continuously positive to other levels, according to 

 the species. In view of the fact that potential difference appears to be a 

 characteristic property of physiological axes, it seem rather improbable 

 that no definite relation between it and other axial characteristics exists. 

 Moreover, comparison of the apical regions and of the manner in which 

 hydranths are reconstituted in the hydroid species in which potential 

 differences have been determined suggests that apical galvonometric nega- 

 tivity may be associated with activity of differentiated or differentiating 

 hydranths or with the stimulation following section and apical positivity 

 with predominance of growth activity. Again, assuming that current re- 

 sults from the potential differences, the current may have different effects 

 on regions which it reaches, according to the sign of the apical region. A 

 current resulting from galvanometric negativity of the apical region or 

 cut end may conceivably result in activation and dedifferentiation of cells 

 which it reaches and organization of a hydranth primordium from a part 

 of the stem without outgrowth, as in Tuhularia (see Fig. 13) ; and current 

 from an electropositive end may establish a growth gradient, such as ap- 

 pears in Ohelia. According to Barth (1934a), inhibition of reconstitution 

 by an applied current may occur at either cathode or anode according to 

 species; and in Tuhularia, according to current density. It is to be ex- 

 pected that reconstitution will be inhibited, either by inhibition of the ac- 



