479 
gregarious and consequently, if one of their number becomes infected in 
the winter quarters, then many must inevitably fall victims to the 
disease, but obviously there is less danger from rodents which live 
underground and apart from human habitations than there is from 
those dwelling in the houses themselves. It is for this reason that during 
winter epidemics a very large number of infected rats, as compared with 
human patients, is encountered. 
The weak rodents are constantly menaced and frightened by the strong 
ones, so that the individuals which have been attaked by plague must 
maintain constant vigilance so as to be able to flee from their pursuers. 
As a weak rat has not sufficient strength to climb a fence or to reach any 
considerable height it is obliged to wander on the surface of the ground, 
thus providing for the spread of plague. 
The large number of children who are infected by playing on the 
ground would seem to emphasize the fact that in this situation the ba- 
cillus is most readily encountered. The following table shows the number 
of children infected with plague during the winter epidemics: 
| | 1905. | 
| | | | 
Number of patients. aes ea a aa ls eee a 
| | | Kobe. | Osaka. | 
Bet —|——_____ —| 
Potelipatien teat = aa wene eee e LAE ca | Lad nee ae een 144 | 90 134 
PAtienisMuderalo Veats weve ee Meee ween es) aoe ol 56 | 36 | 51 | 
Percentage 2224. ee oe Wh is od) tk 38.8 | 40.0 38. 06 
——_ _ eee aE a —— Pie Ss 
From the above it will be seen that the number of patients under 15 
years of age is more than one-third of the total. (See also Pl. Tt.) 
The subterranean and gregarious habits of rats, the sowing of the plague 
germ on the ground, and the large numbers of young patients—all of 
these are closely connected with winter epidemics. 
It is apparent that measures for killing rats must of necessity involve 
the application of biological knowledge bearing on the habits of these 
animals, but our knowledge in this respect has yet to be perfected. The 
methods of destruction used in Japan to-day consist in the use of poison 
or of traps. Such means have only a temporary effect and the results 
of their use can not be considered to be of sufficient permanence to root 
out the evil. The destruction of rabbits in Australia was undertaken 
in such a way as to produce a permanent effect and we have much to 
learn from the method involved. It was based on the fact that the rabbit 
is a polygamous animal and therefore if as many females as possible 
could be destroyed by artificial means, the end would be a struggle among 
the males for their possession. The result of such a practice, of course, 
can not be expected in a brief period, nevertheless it is of a permanent 
character. TI suggest that something of this nature be planned for the 
destruction of the rodents. 
