A. Balfour 
289 
other hand, encountered Ctenophthalmus agyrtes which they did not come 
across. This is probably because some of our rats came from rural districts, 
as was the case with those searched by Nuttall, Strickland and Merriman 
during their investigations in East Anglia. 
To Hirst (1914) we owe information regarding the Acari found on the 
brown rat in Great Britain and the description of a species which was new 
at the time he w~rote. 
The only other papers to which allusion need here be made are those by 
Moll (1917), “Animal Parasites of Rats at Madison, Wisconsin,” which con¬ 
siders only ecto-parasites and helminths, and the Presidential Address of 
Cleland (1918) to the Royal Society of New South Wales in which the author 
enters fully into the question of rat parasites but which is merely of the nature 
of a review of the subject. 
At the time Shipley wrote little was known about the intestinal protozoa 
of the rat but of recent years attention has been directed to the matter. 
\\ e give a list of six parasites of this class which were encountered by us both 
in black and brown rats. Shipley’s list of helminths is now very much out of 
date, as much work has been done on the worms of rodents in general and of 
rats in particular, and it will be found that the present investigation has revealed 
the presence of a new cestode and has been of interest in other directions. 
The study of haematozoa has not been very fruitful but has demonstrated the 
presence of Hejpatozoon muris in the leucocytes of the black rat in this country. 
Apparently the only work following closely the lines we adopted is that 
of Splendore, but it deals primarily with parasites of the field vole Pitymis 
savii Selys. Incidentally he mentions the parasites, ecto-parasites, haematozoa 
and helminths, which rats share in common with this animal. His observa¬ 
tions are of an extensive nature and refer also to bacteria, fungi and intestinal 
protozoa. 
Collection and Technique. 
The rats were for the most part collected from the dealers’ shops where 
they are kept in large cages, each cage containing a number of animals. They 
had been captured comparatively recently, but as a rule had been in captivity 
for some hours or even for several days prior to purchase, and were accordingly 
“sweated.” As Newstead and Evans have pointed out in their “Report on 
Rat Flea Investigation in Liverpool,” such sweated rats are apt to lose their 
fleas, so that it is possible that the number of ecto-parasites, and more especially 
of fleas, did not quite represent all those originally present on their hosts. 
The latter were transferred from the dealers’ cages to perforated tin cases, 
one rat being placed in each tin, and so conveyed to the laboratory where they 
were chloroformed in the tins and weighed as soon as dead. Any ecto-parasites 
which had left their hosts in the tins were collected. These proved to be chiefly 
fleas and were not numerous. Thereafter the fur of the rat was carefully combed 
with a very fine comb, special attention being paid to the neck region and the 
point of junction of the limbs with the body on the under-surface of the 
