Response of Fish to Direct Current — MORGAN 
483 
1885 by Hermann. He reported that tadpoles, 
when in a field of direct current of proper 
strength, would react by orienting themselves 
with their heads toward the positive pole. 
Since that time, experiments have been con- 
ducted with numerous animals, including 
crabs, fish, and frogs. Practically all types of 
animals tested show an orientation to the 
current. Many protozoans, however, orient 
and migrate toward the negative pole rather 
than the positive (Heilbrunn, 1948: 597). 
Considerable research has been done in an 
attempt to explain the physiological reasons 
for this reaction (Breuer, 1905; Scheminsky, 
1924; Van Harreveld, 1937). However, these 
reports indicate that it is still imperfectly un- 
derstood. As nearly as can be determined, no 
satisfactory explanation of this phenomenon 
has been given. 
I wish to express my appreciation for the 
advice and assistance given by Dr. A. L. 
Tester in the preparation of this manuscript 
and over-all supervision of the investigation. 
METHODS 
The period covered by the investigation 
here reported extended from May, 1950, to 
March, 1951. Work was begun at the Hawaii 
Marine Laboratory on Coconut Island and 
continued there throughout the summer 
months. At the beginning of the academic 
year, all the equipment was transferred to the 
Waikiki branch of the Hawaii Marine Labor- 
atory. This branch, operated in conjunction 
with the Honolulu Aquarium, offered certain 
advantages over the previous site, principally 
its proximity to the University of Hawaii. All 
the detailed experimental work reported in 
the following pages took place at the latter 
site. 
Power Supply 
The generating equipment was selected to 
give the widest possible range in current and 
voltage while still being portable and of 
standard design. 
As direct current was more likely to pro- 
duce the reaction desired, an Onan two- 
cylinder, gas-driven, air-cooled, portable-type, 
direct-current, motor- generator set was pur- 
chased. It was rated at 5,000 watts (21.8 am- 
peres at 230 volts). Special equipment in- 
cluded a voltmeter, ammeter, rheostat, and 
circuit breaker. 
Electrodes 
The high conductivity of the sea water 
caused serious overloading of the generator. 
Plans for overcoming this difficulty centered 
around the use of rheostats and suitable elec- 
trodes. However, the rheostat installed to con- 
trol the voltage and current was ineffective 
and various other resistors devised to control 
the current flow proved unsatisfactory. A spe- 
cial electrode was finally developed for use 
during the experiments. This consisted of a 
carbon rod 6 inches long and !4 inch in dia- 
meter inserted into a plastic tube (Fig. 1). 
The size and number of holes in this tube 
governed the flow of current. In effect the 
column of sea water inside the tube became 
the electrode, as the area of this column in 
Copper clamp, adju.s'table 
Su-pporlri ng wire 
#14 Insulated wire t-o 
Wat-erproof ‘i nau.lai^ing compound 
Wirs and solder 
Carbon electrode , 6" long -2^ diam. 
■plastic tube, 12" long — l" diam. 
Fig. 1. Electrode design. 
