PERCENTAGE PERCENTAGE 
<u cm ro 
Figure 145. — The influence of sex and social rank on the transition of the prime pelage into the thinning or senescent state. 
These figures are based upon 250 observations for males and 217 for females. The intersection of lines at 277 days is 
the 50 percent point in the transition of prime to senescent state for the larger sample shown in figure 144. 
preceding death. Most of these rats were over 
300 days of age. Some had no recent wounds 
while others had many. 
Several recently dead rats were found which were 
of normal weight and which were without external 
pathology. 
b. Internal strife and cannibalism. Among mature 
rats there was considerable fighting. Males 
received more wounds than females (fig. 122). 
Three male rats, two of which had received 
extensive head wounds, were known to have died 
as a result of fights with other rats. The third 
was found in the Food Pen on a spot of bloody soil; 
all the flesh had been eaten by other rats and the 
skin was turned wrongside out. Two factors are 
important in this case of cannibalism. The rat 
killed had large infected wounds over the lumbar 
sacral region for the previous 2 months. This 
indicated either prior low-social rank, or at least 
marked contention with its immediate superiors 
for social status. The raw exposed area may also 
have served as an additional incentive for other 
rats to attack it. Also, during the night of its 
death the food in the hopper became exhausted; 
238 
