ON THE SUBJECT OF PLAGUE 
371 
catch our fleas for examination ? The simplest way is by means 
of chloroform or Keating’s powder. If collecting from a 
rat, put the rat into a large glass bottle, on the bottom of 
which a little chloroform has been dropped. The fleas become 
anaesthetised and fall to the bottom of the jar, or remain 
entangled in the hairs. As soon as the rat becomes 
anaesthetised it may be removed from the bottle and the 
fleas picked off it and placed in a test-tube. They rapidly 
recover from the anaesthesia, and can be used for experimental 
purposes. I would like to warn you here, if you wish to 
collect fleas from a caged rat, not to expose the cage to sun- 
light ; for fleas dislike the sun intensely, and will leave their 
hosts to seek the shade. This is a point also which I would 
call to the notice of those who are catching rats on a large 
scale in their endeavours to prevent the spread of plague. 
If these cages are carried for any distance in the sunlight 
through a town, they will inevitably be shedding their fleas 
on the way. Verbum sapienti. 
Another method is by the use of animal traps. Thus, 
should we desire to catch P. cheopis in a room, a guinea-pig 
or man would serve as a suitable trap. The guinea-pig is 
allowed to wander about the floor of the room and soon gathers 
up all the fleas present. If the experiment takes place at night 
in a rat-infested room, the bag will be a large one. 
Still another method might be by the use of fly-paper ; 
the ordinary Tanglefoot paper is very suitable. Put a suit- 
able animal in a cage, and all around it for a depth of at least 
6 inches, place Tanglefoot paper. The flea’s maximum hop 
is about 4J inches. Attracted by the animal, the flea will 
endeavour to reach it, and be caught in the process. For 
examination, pick it off and wash in alcohol. 
Examination of Fleas. — Now, having caught our fleas, we 
proceed to examine them. Living fleas may best be examined 
while under the influence of chloroform, and J-inch objective 
of an ordinary microscope is of sufficient power for identifica- 
tion. For examining dead specimens, dissection is employed, 
and, to facilitate this, fleas may be boiled for a short time in 
caustic soda or potash, or allowed to soak in water at 80° F. 
for twenty-four to forty-eight hours. The soft parts of the 
