capturing the rats, all individuals were also 
removed from the artificial harborages. This was 
done by placing a cloth sack over the end of the 
drain tile leading from the harborage box. Upon 
opening the lid of the box the rats usually ran out 
into the sack. The third technique utilized in 
capturing the rats was the excavation of burrows. 
A drain tile with a cloth sack attached was inserted 
into each exit from the burrow system (see fig. 11). 
Then the excavation of the burrow began at the 
center of the burrow system. As it was excavated, 
the open ends of tunnels were kept plugged with 
other cloth sacks. By this process the rats in a 
burrow system were gradually encouraged to leave. 
To do so necessitated their passage through the 
drain tiles into the attached sacks. This procedure 
was mainly resorted to only during the December- 
January 1948-49 period and at the termination of 
the colony. The burrows in the alleys were only 
disturbed at the end of the study. While the rats 
were still in the sacks, each would be grasped just 
back of the head with the thumb and index finger 
of the right hand, while at the same time pressing 
its body down with the remainder of the hand. 
Then the left hand was inserted in the sack and a 
gradual exchange of the rat made from the right 
to the left hand. If one is careful, there is little 
danger in being bitten, even by the larger rats. 
When only identification of the rat was re- 
quired it was immediately released, but if 
other observations were necessary, the rat was 
anesthetized before further handling. 
Routine observations made usually included: 
1 . Weight in grams. 
Figure 1 1 . — Technique for capturing rats at the time of excavating burrows. Here the burrow emanated from the harborage 
box through a hole gnawed through its wall. Drain tiles with cloth sacks attached were inserted into each burrow exit. 
As the burrow is being excavated wads of cloth were inserted into the tunnels. Gradually the rats were forced to leave 
the burrow and enter the sacks as the tunnels were excavated. 
12 
