A. Balfour 297 
No case of rat leprosy was encountered and the absence of neoplasms was 
rather surprising. 
5. MISCELLANY. 
Pregnancies appeared to be commonest from April to June, during which 
period 39*5 per cent, of female brown rats examined were pregnant. There 
seems to be a second breeding period from September to November. July 
and August appear to be off-seasons, as do the winter months from December 
to January inclusive. The numbers examined, however, were perhaps too small 
to allow anv conclusions to be drawn. 
«/ 
SUMMARY. 
1. Attempts to secure a micro-organism which could induce abortion or 
sterility in wild rats and which might be used in an anti-rat campaign, more 
especially when plague threatens a community, have not been successful. 
2. An account, however, is given of certain micro-organisms producing 
pathological conditions in the genito-urinary tract of wild rats. 
3. A routine determination of rat parasites including ecto-parasites, 
helminths, intestinal protozoa and haematozoa has been undertaken. 
4. It has led to the discovery of a new^ species of Hymenolepis and has 
shown that Heligmosomum braziliense is present in rats in England. It has 
also demonstrated the occurrence of haemogregarines in the leucocytes of 
black rats in this country. 
5. Work has been done on the incidence of Leptospira icterohaemorrhaqiae 
in Rattus norvegicus and Rattus rattus in England and on the mechanism of 
its transmission. 
6. It has been shown that apparently the guinea pig may act as a carrier 
of the Leptospira without exhibiting any marked symptoms of the disease 
which the latter produces. There is also some evidence to prove that infection 
may take place through the alimentary tract. 
7. The Leptospira was successfully and easily cultivated in Wenyon’s 
modification of the Noguchi method but in large measure lost its virulence 
as the result of repeated subcultures. Even after a year, however, it was still 
capable of producing characteristic symptoms in the guinea pig. 
8. General pathological conditions occurring in wild rats have been 
recorded. 
9. A few observations have been made on the seasonal incidence of 
pregnancy in wild rats. 
REFERENCES. 
Bacot, A. W. (1919). The fleas found on rats and their relation to plague. .Jovrn. Boy. 
Sanit. Inst. XL. 53. 
Balfour, A. (14. v. 1921). Rat destruction: a suggestion. Lancet, i. 1049. 
Baylis, H. A. (25. iv. 1922). Observations on certain cestodes of rats, with an account of 
a new species of Hymenolepis. Parasitology, xiv. 1. 
Brug, S. L. (1919). De Entamoeben van dc rat. Genee.sk. Tijdschr. Nederlandsch-Indie, liv. 
Part 4. 
