286 
Observations on Wild Rats in England 
(a) + ( b ). Two of the rats infected with (b) died on April 3rd from pneumonia. 
Nothing abnormal was found by the naked eye in their genital tracts which 
were not further examined. The remainder were kept and watched for two 
months to see if any sub-acute or chronic malady resulted. Nothing was 
observed. They were then placed with males. 
All three of the rats injected with (a) had healthy litters, on June 5th, 12th 
and 14th respectively. The third injected with (b), which was placed with a 
male on two occasions, had a healthy litter on July 20th, 1921. Of those 
infected with (a) + (b) two had litters on June 5th and the third was obviously 
pregnant on June 21st. 
Hence organisms (a) and (b) were ruled out of court. 
(ii) Eat 330. Chloroformed May 10th, 1921, and tw r o dead foetuses found 
in the uterus. 
Aerobic cultures from the uterus resulted in the isolation of ( d ), a gram- 
negative coliform bacillus, and (e), a gram-positive coccus. 
The vagina of a tame rat was smeared with material from the uterus of 
Eat 330 on May 11th, 1921, and this animal was placed with a male on 
May 14th. It had a healthy litter on June 11th, 1921. 
Two other tame rats were injected per vaginam with a mixture of a 
24 hours growth of ( d ) and ( e ) on May 12th. They were placed with males 
on May 14th and had healthy litters in due course. 
Apparently, therefore, neither of these organisms was of the type required. 
(iii) Eat 369. Chloroformed June 27th, 1921. Found to have an extra- 
uterine gestation from which cultures were taken. Two organisms were isolated 
(/), a coliform bacillus, and (g) a gram-positive streptococcus. 
Material from cultures of both organisms was introduced into the vaginas 
of two rats on June 28th, in one case by injection, in the other by smearing. 
The smearing method was employed as it was thought it might produce slight 
surface abrasions such as possibly occur during coitus. Both were placed with 
males on June 30th and both had litters. 
Six other white rats were injected per vaginam on July 11th, 1921, with 
a broth emulsion of (/) and (g) and subsequently placed with males. All were 
pregnant on July 29th. In no instance was any ill effect produced as the 
result of injection. 
It therefore appeared clear that organisms (/) and (g) were not of service. 
Having failed to obtain in wild rats under natural conditions any organism 
having the effect desired, attempts were made to infect the genito-urinary 
tract of tame rats with an organism which it was hoped might prove efficacious 
either in producing abortion or sterility. 
The choice was limited, because care had to be taken that any organism 
employed should be of such a nature as to obviate any risk of producing 
serious effects in man or the domestic animals. The ideal would, of course, 
be one which, while capable of producing the desired effect in wild rats, was 
incapable of transmission to man or the domestic animals or, if transmitted 
