306 ELECTRO-PHYSIOLOGY CHAP. 



of the constant current the first effect is usually a momentary 

 arrest of the flow of granules, followed by the sudden protrusion 

 of a hyaline pseudopod from the anterior end of the body, 

 directed in a straight line towards the kathode. In the case of 

 Amoeba limax this powerful pseudopod extends to a considerable 

 length, and draws the entire body-mass into itself, so that the 

 amoeba following the direction of current creeps towards the 

 kathode by degrees, in its normal form. If the current is 

 suddenly reversed during this period, the flow of granules and the 

 progress of the amoeba are reversed in direction with a strong 

 current and it is possible by frequent alternation to obtain con- 

 tinuous movements of the amoeba in opposite directions. It is 

 easy to show that the action in this case is essentially similar to 

 that witnessed in Actinosphaerium, Polystomella, and Pelomyxa, 

 although obvious signs of excitation cannot be detected. If, as can 

 hardly be disputed, we may reckon as effects of excitation the forma- 

 tion of varicosities in the pseudopods, along with their retraction, 

 and the eventual partial destruction of the body-substance, two im- 

 portant conclusions may be deduced from the observations before us. 

 In the first place, the proposition follows, that, like muscle, the sub- 

 stance of protozoa obeys a laiv of polar excitation, in which, however, the 

 localisation (polar distribution) of effects is reversed excitation being 

 at the anode at make, at the kathode at break, of current. Secondly, 

 the fact carries conviction, that the process of excitation is effected 

 not merely at the moment of commencement and cessation of current, 

 but proceeds throughout the whole period during which the current 

 is passing, and for a short time after it has been broken. This 

 excitation does not produce contraction as in muscle, but sets up 

 a centripetal backward" flow of the protoplasm, which under 

 certain conditions may lead to local destruction of the outermost 

 layers. The various phenomena connected with the final disinte- 

 gration in various forms are sufficiently intelligible from the 

 different composition and consistence of protoplasm in each 

 particular case. Under certain conditions e.g. in Amoeba 

 visible changes of form are altogether absent; the excitation remains 

 " latent." But even then the direction of movement of the 

 entire body -mass gives cogent evidence of the existence of polar 

 excitation, and it is quite intelligible that such excitation should, 

 under certain conditions, give rise to an axial disposition of the 

 body of the proteid. In the first place, we find that other 



