METABOLIC GRADIENTS IN AMOEBA 57 



cathode. Since the anterior ends of Protozoa are more suscep- 

 tible to cyanide than other levels of the body, it is practically 

 certain that a difference of potential exists in them like that 

 discovered by Mathews for coelenterates, and that therefore 

 their anterior ends are electro-positive (internally) to the rest 

 of the body. This would account very simply for their behavior 

 in the electric current. The earthworm may be said to be es- 

 pecially devised by nature to furnish a crucial test for this ex- 

 planation. It has recently been found that when the earthworm 

 is subjected to the current, it bends itself into a U-shape and 

 travels toward the cathode with anterior and posterior ends 

 directed to the cathode and middle region directed to the anode. 

 Clearly a fundamental relationship exists between electrical 

 currents in living matter and susceptibility; and it is reasonable 

 to suppose that both are referable to the same cause. 4 



The axial gradients may also be demonstrated indirectly by 

 the use of proper non-lethal concentrations of the same substances 

 as are employed in the direct method. Differential inhibitions 

 and accelerations of growth, development, regeneration, etc., 

 along the principal axes are thus produced. Particularly illu- 

 minating are the experimental modifications of development, 

 resulting in a great variety of predictable teratological embryos 

 and larvae (Child, '16 c and much unpublished work). 



Regarding the explanation or interpretation of the suscepti- 

 bility gradients, a few words must suffice here, as this matter 

 has been discussed at length in many of Child's papers. The 



4 The existence of these permanent differences of potential along the axes of 

 organisms (they have long been known in plants, also) can-scarcely be explained 

 on the basis of the depolarization theory of Lillie ('14, '15, '16) and others. Ac- 

 cording to this theory, stimulation causes a local change in the electrical condi- 

 tion of the surface (a depolarization of the surface) ; the stimulated area thus 

 becomes electrically different from neighboring unstimulated regions, and this 

 difference of potential is the cause of the origin of an electric current, flowing 

 (externally) from the unstimulated to the stimulated region. According to this 

 idea, all bielectric currents originate in this way. I am unable to see how this 

 theory could be applied to permanent differences of potential such as I am 

 referring to; they almost certainly are of metabolic origin, and are the incidental 

 result of the metabolic gradient. Their similarity to other bioelectric currents 

 would indicate that all such currents originate in metabolic (i.e., chemical) 

 differences and are merely incidental to the presence of such differences. 



