PRIMARY INHIBITION OF CILIARY MOVEMENT 427 
The galvanic current produces primary stoppage in all the 
swimming plates only when it is sent through the animal in a 
longitudinal direction with the cathode outside the sensory pole 
(‘longitudinal oro-central current’). In experiment 3 it was 
determined, by continually increasing the strength of the current, 
where the threshold, expressed as density of the current, lies for 
the galvanic inhibitory effect. In an animal 23 mm. long at a 
temperature of 17°C. it was found that the lowest density of 
current with which a total stoppage of the swimming plates 
lasting 5 seconds was attained lay between 1.47 and 1.60 
m.amp./em.2. In a number of specimens, however, without a 
direct threshold determination having taken place, total inhibi- 
tion appeared with a considerably lower density of current, e.g., 
in experiment 2 with 0.77 m.amp./cm.? in a 26-mm.-long animal 
at 16°C. The total inhibition that can be attained with a gal- 
vanic current of the order of magnitude just mentioned is limited 
in time and usually does not last more than a minute. In experi- 
ment 8 there are more exact determinations of time which show, 
in addition, that the inhibition may have a different duration in 
different rows of the same animal. 
The primary inhibition when a galvanic current is transmitted 
originates from the cathode. This is shown in a particularly’con- - 
vincing way by experiment 10. In an earlier work I have put 
forward additional proofs of this, obtained from experiments with 
a transverse transmission of the current, when the anode and 
the cathode have been situated in the equatorial plane of the 
animal outside two diametrically opposite rows. In these experi- 
ments primary inhibition took place at the cathode with so weak 
a current that it did not exert any inhibitory effect at the anode; 
with a considerably stronger current, an inhibitory effect appeared 
at the anode, but this was secondary, due to contraction of the 
animal’s body there. 
The transmission of a longitudinal current with the cathode 
outside the oral pole (‘centro-oral current’) evokes, when the cur- 
rent is rather strong, an inhibition, which is, however, chiefly 
secondary, due to a contraction of the animal’s aboral part situ- 
ated nearest to the anode (experiment 1). That, however, even 
