288 
Observations on Wild Rats in England 
In the second instance two female rats showing early signs of pregnancy 
were used and the walls of the vagina were thoroughly smeared with a 24 hours 
culture of the two strains of this diphtheroid organism. Both of these rats, 
however, had healthy full-timed litters thirteen and seventeen days later 
respectively. 
It is fully recognised that these experiments were conducted on a very 
small scale. This was largely due to the extreme difficulty of procuring tame 
rats from dealers in London during the earlier part of 1921. The results, how¬ 
ever, at any rate with the diphtheroid organism, are in accordance with those 
obtained by Teacher and Burton ( Journal of Pathology and Bacteriology , 
xx, 1915, p. 14) who found that the introduction of cultures of this organism 
into the vaginas of guinea pigs were negative. 
Although the record of these experiments appears scanty the work itself 
involved a great deal of time and labour and it is unfortunate that nothing 
definite resulted from it; still, negative results possess a certain value and it 
seems desirable to draw attention to the matter in case others, perhaps dif¬ 
ferently situated, may care to carry out further investigations. It was not 
possible to conduct the enquiry on as large a scale as we originally con¬ 
templated, but the failure to recover any efficient organism from wild rats and 
the paucity of pathological conditions in the genitalia of these animals militated 
against the success of the work. It is conceivable that in the tropics conditions 
are different and that a research on these lines might prove more promising. 
2. DETERMINATION OF PARASITES IN RATS. 
This was taken up as a matter of routine although no very novel results 
were expected, as the field has already been covered by various observers. 
At the same time, so far as I am aware, no work on precisely the same lines 
has been undertaken in this country. Shipley, in 1908, published a useful 
paper on “ Rats and their Parasites,” in which he gave a list of all the various 
kinds of parasites found on and in rats but this applied to other parts of the 
world as well as England. 
So far as fleas are concerned the most complete account is that by Bacot, 
1919. His paper included two lists, one of all the fleas found on rats up to 
that date in all parts of the world, the other confined to fleas found on rats 
in Britain. It will be seen (vide infra) that we found only four of the eighteen 
species he records. Doubtless this is due in part to the fact that the great 
majority of our rats came from London and nearly all of them from towns. 
As Bacot points out, rats are probably the true hosts of only seven or eight of 
the species he mentions. 
Newstead and Evans (1921) determined the species of fleas found on rats 
in Liverpool and identified Xenopsylla cheopis, Ceratophyllus fasciatus, Lepto- 
psylla musculi, Ceratophyllus londoniensis and Ctenocephalus canis. The first- 
named was found chiefly on ship rats and Leptopsylla musculi was most 
prevalent on rats from the dock area. We did not find this flea but, on the 
