C. Strickland and Cl. Merriman 
O 
*J 
Methods. 
Collecting the fleas from rats. It was necessary for the purpose of 
our investigation to accompany the official rat-catchers of the Local 
Government Board into the field so as to obtain an accurate flea-census. 
Although trapping was extensively used, most of the rats wei’e captured 
by ferreting their runs. We were obliged to be present when they 
were killed because as soon as a rat dies the fleas begin to abandon it. 
It is, therefore, essential that the fleas should be collected immediately 
upon the death of the host if a true estimate of their number is desired. 
The outfit for collecting consisted of: 
(a) Clean calico bags with string attached. 
{h) Fine forceps and camel-hair brushes. 
- (c) Small corked tubes containing 50 “/o spirit carried in a box 
provided with holes for the reception of the tubes. 
{d) Slips of paper, which were duly numbered in pencil and 
dropped into each tube, in accordance with the numbers given to the 
rats. 
The rats, immediately upon being killed, were dropped into the 
bags, which were firmly tied up to prevent fleas from escaping. The 
bags containing the rats were subsequently placed in tins and a little 
chloroform was added before closing the lid. The fleas now abandoned 
their hosts and died after a few minutes, so that they were easily col¬ 
lected upon opening the bag. Fleas from each rat were put into a 
separate tube for subsequent examination. The method we have 
described ensured our obtaining an accurate flea-census based upon the 
numbers and species of fleas found upon each rat. 
Determination of the fleas. The fleas found upon the rats were 
determined by microscopic examination, a Zeiss binocular dissecting 
microscope being used for the purpose. For examination it is best to 
render fleas transparent, and this is most conveniently effected by 
placing them in strong phenol solution, after drawing off the alcohol in 
which they are preserved. They may require 24 hours to clear, after 
which they may be transferred for some minutes to clove oil and thence 
to balsam if permanent mounts are required. The clearing process 
renders the internal structures of the male and female genital organs 
visible through the chitinous integument, whilst the external segments, 
which are also of specific importance, remain clearly visible. 
The Rat. All the fleas which we examined came from Mus 
decumamis. It is well known that it is a difficult matter to catch many 
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