Figure 5. — View of ihe pen from the tower in February 1 949 looking toward the north corner. 
Corps. 
Photograph by U.S. Army Signal 
to 36 as shown in figure 3. Although the boxes 
were of 1-inch thick wood the removable tops 
were given further protection with a sheet of 
insulation board. The only place that rats were 
not allowed to dig burrows was in the Food Pen. 
These were regularly destroyed shortly after they 
were formed. Elsewhere in the pen burrows con- 
structed by the rats were rarely disturbed. 
The division of the pen into definite tracts which 
might affect the behavior of the rats was accom- 
plished by the establishment of two internal barrier 
fences. The first was the fence forming the Food 
Pen. The second barrier fence was parallel to the 
first and 20 feet distant from it. As may be seen 
in figure 3, this latter barrier fence served to pro- 
duce a band about the Food Pen 20 feet in width 
in which no artificial harborage was provided, 
while at the same time it separated off a triangular 
area in each corner of the main pen. A 3-inch 
diameter passage was placed through this barrier 
fence at the points where the corner triangular 
areas adjoined. This system of barrier fences and 
passages through them provided for alternate 
equivalent-length routes of travel. A rat starting 
from the center of one of the triangular areas and 
going to the Food Pen could leave the triangular 
area through the passage at either the left or the 
right end of the base of the triangle formed by the 
barrier. At this passage the rat would find itself 
equidistant from two passages leading through the 
barrier fence into the Food Pen. The purpose of 
this provision for alternate choices in travel was 
that, in the eventuality of a passage being defended 
or blocked by one rat, a second rat approaching 
this passage would have an alternate route for 
attaining its goal. The goals in question at either 
end of the routes of travel were the source of food 
and the source of harborage. 
7 
