SCIENCE AND INDUSTRY. 
adopted which would, in effect, with certainty gradually reduce the 
number of females, success would be assured, for it is almost certain 
that the time would arrive when the males would co-operate in complet- 
ing the process of destruction. Rodier claims that by the present 
methods more males are caught than females, with the result that those 
not caught live in a polygamous state. Because of being polygamous, 
the females are more prolific than they otherwise would be, and produce 
more females than males. The way to exterminate rats is to make and 
keep them polyandrous—that is, the males in excess of the females; 
and the way to do this is to catch the rats alive and uninjured, kill the 
females, and liberate the males. When this is done, the males will 
persecute the females that are not caught, and.thus prevent breeding. 
They will also kill the newly born, and when they largely exceed the 
females in numbers they will worry the remaining ones to death. By 
this means all the females will-be exterminated, and the males remaining 
will finally die of old age. The greater the excess of males, the quicker 
the extermination. ; 
To put into operation such a. scheme, it would be necessary for all 
rat-infested premises to be thoroughly equipped for the purpose of 
catching rats alive and uninjured. Furthermore, large numbers of 
rat-catchers would have to be employed to regularly visit such premises 
for the purpose of separating and killing the females and liberating the 
males. 
Again, it would be equally essential for all districts to be operating 
continuously in the same direction. Otherwise, having regard to the 
migratory habits of the rodents, the scheme would be hopeless. Were 
it shown that destruction by baiting accounted for as many females as 
males, then, providing the “ Rodier” method were found practicable of 
universal application, a combination of the two methods would be well 
worth consideration. Before considering the application of any such 
should be thoroughly investigated, not only by specially designed experi- 
ments, but also as to whether its application could be properly maintained 
throughout the country. In the opinion of the author, even were the 
method proved theoretically correct, it would probably fail for want of 
co-operation, for there are few people who either care to handle rats, 
detain them on their premises alive, or liberate those already secured. 
The methods of destruction may be described under the following 
headings, namely:—Baits, Poisons, Gassing, Trapping, Hunting, and 
Virus. 
Barrs. 
It is commonly believed that faint traces of the oils of rhodium and 
aniseed attract rats. It has been proved, however, that instead of 
improving the bait they have the contrary effect. And of all the baits 
tested, the one that has been found most readily accepted is dry bread. 
The tastes of brown and black rats have been found to be practically 
identical, and the following table will serve to illustrate the merits of the 
various foodstuffs used as bait in experiments carried out within the 
Zoological Gardens, London. ‘The percentages given are based on the 
294 
scheme, however, it would be desirable that the probability of its success - 
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