A. Balfour 
285 
Of 217 female brown rats examined 32 were found to be pregnant, litters 
varying from 1 to 12, the average in 27 cases where an estimate could be made 
being 7. 
1. BACTERIOLOGICAL EXAMINATION OF RATS. 
After opening the abdomen, organs from which bacteriological preparations 
were made and cultures were taken were seared on the surface and incised 
with sterile instruments under aseptic conditions. At first in the case of 
female rats cultures were taken in every instance, save when the animal was 
pregnant, from the upper portion of the vaginal tract or from the uterus and 
incubated both aerobically and anaerobically. 
A number of different organisms, both cocci and bacilli, were isolated which 
could be grouped according to their sugar reactions. As nothing of any 
practical interest was found, either by these fermentation tests or by sub¬ 
jecting the organism isolated to serological tests (i.e. organism versus blood 
serum of host, organism versus serum of other rats or organism versus group 
high titre serum), this routine was discontinued and attention directed solely 
to the recovery of organisms from the genital tracts of female rats which 
exhibited definite pathological changes. 
There were only four instances of this kind, three of which were fully 
examined. One was a case of pus m the Fallopian tubes in a non-pregnant 
rat, two were cases in which the uterus contained dead foetuses, the fourth 
an example of extra-uterine gestation. 
The protocols of the three cases examined are as follows: 
(i) Rat 207. Non-pregnant. Pus of a cheesy character present in the 
uterus and in both Fallopian tubes. 
On aerobic culture from this pus two organisms were found, i.e.: (a) a gram¬ 
negative coccus and (b) a gram-positive streptococcus. 
Cultures of both these organisms were inoculated together intraperitoneally 
into an apparently healthy mouse, which died in 24 hours. A blood culture 
from the heart of this mouse revealed the presence of another organism (c) 
while the original (a) and (b) were not recovered. Organism (c) was eventually 
proved to be B. enteritidis Gaertner. A culture of this organism before it had 
been definitely identified was introduced into the vagina of a tame rat on 
January 21st, 1921. The animal died on February 17th, 1921, and it is inter¬ 
esting to note that the bacillus was recovered not only from the heart-blood 
but also from the Fallopian tubes. Various other passages were carried out, 
both in the case of male (preputihl infection) and female rats but as the 
organism was eventually found, as stated, to be a species pathogenic both to 
man and animals and hence unsafe to use for our purpose, further work with 
it was abandoned. 
Organisms (a) and (6) were inoculated separately intraperitoneally into 
laboratory mice on February 16th, 1921. No ill effects were produced. On 
March 16th, 1921, three rats were given a vaginal injection of («), three rats 
were given a vaginal injection of (b), three were given a vaginal injection of 
Parasitology xiv 
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