deenergized barrier while the second counter is designed to record the
number of shocking pulses delivered by the fence charger. Thus, rat
activity can be measured prior to electrification of a fence for later
comparison with the number of shock pulses actually delivered.

Coulometric event counter problems corrected

Two years ago, specialized coulometric event counters were designed
and sent to the Philippine field station for use in measuring and
evaluating rodent activity during field baiting tests. However, a
puzzling, intermittent functional problem developed. The problem has
now been resolved and the units repaired. Apparently, the high rela-
tive humidity in the Philippines reacted with the encapsulating mate-
rial and interfered with the functioning of the apparatus.

Chemical analyses of Philippine ricefield samples for diphacinone and
warfarin residues

Analytical methods for diphacinone and warfarin, which were developed
at the DWRC, are being used to study possible accumulation of these
chemicals in various types of ricefield samples. The analyses are
being performed to determine whether residues might occur in rice
plants, rice grains, soil, and water samples following intensive
application of the chemicals (see page 36). Analyses of water samples
have been completed. Diphacinone was not found in any of these.
Warfarin was found at very low concentrations, ranging from 0.01 to
0.02 ppm, in some water samples from fields receiving the highest rate
of application. Analyses of the plant, grain, and soil samples will
be made after sensitivity and recovery standards have been established
for each type of material.

A potential new wildlife marking agent

Several aspects of vertebrate damage control investigations, as well
as other types of wildlife research, would benefit from improved
methods for marking animals and toxic baits. DWRC scientists have
been experimenting with a new and promising wildlife marking tech-
nique. The following report describes the agent and a series of
experiments designed to examine potential uses.

Small plastic particles called "microtaggants" were originally devel-
oped by the 3M Company to provide a means of identifying the type and
origin of explosives used in criminal activities. They have proper-
ties which make them suitable for use in bait formulations or as a
topical (surface) marking agent. Microtaggants are irregular flakes,
all of which will pass a 425-p screen. Colored layers in the parti-
cles form a code which can be read with a 30X or greater optical
magnifier. The number of layers used ranges from five to seven and