BY DR. A. JEFFERIS TURNER, M.D. LOND., D.P.H. CAMB. 119 
evidence from which we know that plague is propagated 
by Pulex cheopis :— ! 
(1) Two wire cages are placed in a glass box. The 
cages rise above the level of the box, and both box and upper 
portion of cases are covered with fine muslin impervious to 
fleas. In case A. is placed a rat inoculated with plague, 
together with 10 to 20 living Pulex cheopis. As soon as 
the rat is dead, a healthy rat is placed in cage B. There 
is no direct contact between this and the first rat, nor with 
its excretions. The rat in cage B. develops plague. Some 
of the fleas are to be found on rat B. on examination. This 
experiment has been repeated many times. 
(2) A rat is inoculated with plague. After death, 
it is searched for fleas. These are caught and transferred 
to a flea-proof cage containing a healthy rat. The latter 
dies of plague. On it are found some of the fleas, and in 
the fleas are plague bacilli. This experiment has been 
repeated many times. 
(4) Simond, Gauthier and Rayband, and Liston never 
succeeded in infecting animals from one another when 
healthy and plague-infected animals were confined together 
in the same cage if fleas were excluded, and if the animals 
were not allowed to devour the bodies of their dead comrades. 
The recent Indian Commission verified this on a large scale. 
Fifty healthy guinea-pigs were confined with ten inoculated 
with a plague culture under flea-proof conditions. The 
latter all developed plague, but none of the former. The 
same experiment was repeated. One of the unindculated 
animals developed plague. The animals were examined, 
and one rat-flea was found. The other forty-nine uninocu- 
lated escaped. Forty-nine guinea-pigs were confined, with 
ten inoculated guinea-pigs, rat-fleas being known to be 
present. In seventeen days, every guinea-pig was dead 
of acute plague. From the last two animals four-hundred 
fleas were recovered. And so on with similar experiments. 
For instance, guinea-pigs placed in a cage in a compartment 
where a guinea-pig plague epizootic was in _ progress, 
frequently contracted plague if the cage was suspended 
two inches from the floor, and fleas were found on them ; 
but if suspended two feet from the floor, remained free from 
both plague and fleas. The rat-flea cannot jump two-feet 
