a difference of potential is maintained between the proto- 
plasmic surface and that of the medium (indicated by the 
small + and — signs).* 
Just as in the analogous case of the capillary electrometer 
(section 2), the effect of a current travelling from A to K will 
be to diminish the contact difference of potential at points 
such as a, which form the physiological anode, and to 
increase it at points such as k, which form the physiological 
kathode. 
Therefore, as we have seen (section 2), the effect will be 
to increase the surface tension at points such as a, and to 
decrease it at points such as k. The surface, and, conse- 
quently, the volume en the kathodic side of the organism will 
therefore increai^e^ while on the anodic side they will de- 
crease. The organism will, therefore, move over towards the 
kathode, as indicated oy the arrow — it will be "negatively gal- 
vanotactic." Consider now the effect of a similar current 
upon a ''negative" amoeboid organism : that is, one which is 
laden with anion-proteid, so that the difference of potential 
between the protoplasmic surface and that of the medium is 
as represented in the diagram. In this case the contact dif- 
ference of potential will be increased at the physiological 
A( + ) TZa h'.\l (-)'< 
<■ 
Figure 2. 
anode, and decreased at the physiolosfical kathode ; hence, 
reasoning as before, the organism will move towards the anode 
— it will be "positively galvanotactic." The effects upon 
ciliated organisms will be similar, for if the diagram repre- 
sents one of the cilia of a "positive" organism subjected to a 
constant current in the sense indicated, the P.D. (difference of 
* As siioh organisms are electro-pn.sitive to tli^ solution in 
which they are siifspended. I will in the future distinguish them 
as "positive," those which are laden with aniou-proteid being 
designated "negative." 
