12 



I. H. HYDE. 



face tension. The direction and distance of the movement de- 

 pends of course upon the strength and direction of the current 

 introduced into the active pipette. When the mercury is brought 

 to the tip of this, the pressure clamp is closed, the mercury held 

 near the top, which may end in a drop of the same solution that 

 surrounds the organism that is to be stimulated. 



If the active electrode be cathodal, a stimulus of a minimal 

 break shock will stimulate, for instance, the stalk or any desired 

 part of a Vorticclla, that is in the hanging drop, and near contact 

 with the active electrode, and the effect of the stimulation is 

 observed under the microscope. 



A diagram of one micro-electrode is shown in Fig. I. The 

 pipette holder and moist-chamber are omitted in the illustration. 



H 



b H 



d 



FIG. i. a, battery; b, commutator; c, induction coil; d, clamp; e, platinum 

 wire; /, tip of pipette; g, clamp; /;, rubber tubing. 



The movements of the mercury due to changes in surface ten- 

 sion by a force sufficient to overcome capillary attraction, in- 

 augurated by the passage of an electrical current, made it pos- 

 sible to employ this devise as a capillary electrode. 



The fact that the meniscus of mercury moves more or less in 

 either direction in the tip of the micro-pipette by altering the 

 strength and direction of the current, and thus ejecting a solution 

 that lies between the mercury and the tip of the micro-pipette, or 

 drawing in a solution due to suction, led to the idea that it could 

 be adapted for the injection or extraction of minute quantities 

 of substances from unicellular structures. But the mechanism 

 needs further improvements before it can be satisfactorily em- 

 ployed for very accurate work. 



I therefore was agreeably surprised while this paper was going 



