80 PHYSIOLOGY CHAP. 



some animals it is possible to transform positive into negative 

 heliotaxis, and vice versa. 



XL Electrical stimuli are those most frequently adopted by 

 physiologists for the excitation of living matter. Their action on 

 muscle and nerve will be treated at length in another connection. 

 Here we must confine ourselves to the effects of electrical excitation 

 on unicellular organisms. 



Kiihne and Engelmann were the first who investigated this 

 subject. They both found that after weak induction shocks the 

 amoebae suspended their locomotor movements; with stronger 

 shocks the pseudopodia assume a globular form ; if the shocks were 

 still further strengthened, electrical tetanus resulted, followed by 

 a kind of coagulation of the protoplasm, which was shared by the 

 nucleus. Galvanic currents also, in proportion with their intensity, 



FIG. '23. Kathodic galvanotaxis in a drop of water with paramoecia. (Verworn.) c, on closure 

 of current, the paramoecia swim in curved lines to approach the kathode ; l>, paramoecia 

 collected round the kathode. 



produced a partial or total contraction of the protoplasm of 

 amoebae. 



Verworn discovered a directive action of the galvanic current 

 analogous to that produced by other stimuli, which he terms 

 galvanotaxis. He particularly investigated certain species of 

 ciliated infusoria, e.g. Paramoecia. When immersed in a drop of 

 water through whicli current is passing, these infusoria flock to 

 the kathode in wavy movements which are more pronounced in 

 proportion as the current is weaker. On breaking the circuit the 

 Paramoecia scatter themselves again uniformly through the drop 

 of water (Fig. 23). This is not a case of kataphoric action, i.e. of 

 mechanical transport in the direction of the current, such as might 

 occur with non-living particles, because the infusoria would then 

 swim in a straight line, and move more rapidly, with no orientation 

 of the principal axis of the body. Moreover, chloroform or ether 

 paralyse these movements, which would not occur if they did not 

 represent physiological phenomena in living beings. Budgett and 

 Loeb noted that these same Paramoecia moved to the anode if the 

 water which contains them is replaced by a 0*4-0*7 per cent 

 solution of sodium chloride. 



