A. Balfour 
283 
A suggestion has already been made to the effect that its value might be 
determined by experimental work on ship-board but so far nothing has been 
done in this direction. The method has certain drawbacks. It is not easy to 
handle wild rats; only a professional rat-catcher or someone with special 
experience can do so with impunity. Again it is by no means always easy, 
in the case of young specimens, to determine the sex. 
In thinking matters over the idea occurred to one that if only some 
bacterial agent could be found which would either produce sterility in rats 
or induce abortion it might be possible to employ it to advantage and in such 
a way that the male rat might infect the female.during the sexual act. 
It was clear that in the first place it would probably be difficult to find any 
such organism which could be safely used and in the second that even if it 
were forthcoming and proved pathogenic only to the rats there was every 
likelihood that the rodent would soon develop an immunity against it. Still 
a research of this nature appeared to offer some possibilities, for it is easy 
to understand how useful a wholesale interference with the rat’s family life, 
even for a limited period, might be if the rat population were found harbouring 
B. pestis and there was a danger of an outbreak of human plague. 
It appeared, therefore, worth while to set such an enquiry afoot, especially 
as, during its course, other matters of interest and importance could con¬ 
veniently be studied. 
Eventually a system of team work was evolved with a view to collecting 
information on the following points: 
1. The possibility of obtaining, either from rats themselves or from some 
outside source, an organism which could be safely used on a large scale for 
producing sterility or inducing abortion in rats and which could be transmitted 
from the male to the female rat and possibly also conversely during coitus. 
2. The occurrence of rat parasites, including ecto-parasites, helminths, 
intestinal protozoa and haematozoa. 
3. The incidence of Leptospira icterohaemorrhagiae and the mechanism of 
its transmission. 
4. The presence of pathological conditions, apart from those associated 
with the genito-urinary system, in the rats examined. 
5. Any other matters of general interest regarding the rat population as. 
for example, the relation of the pregnant state to season. 
At the outset I wish to point out that personally I have been but little 
associated with this research work. Indeed, for a large part of the time during 
which it was being prosecuted I was abroad, but as 1 initiated it and have been 
more or less in touch with it throughout it has been considered advisable that 
I should place the results, such as they are, on record. 
The main object of the enquiry was in the hands of Major H. C. Brown who 
was entrusted with the bacteriological work. Lt-Colonel G. E. F. Stammers 
performed most of the post-mortem examinations on rats, examined blood 
films, and kept a record of the findings. 
