866 SOME POINTS OF GENERAL INTEREST 
All varieties of rats can be infected with the greatest ease, 
and Albrecht and Ghon, of the Austrian Plague Commission, 
have shown that by smearing plague material upon the intact 
shaven skin of a guinea-pig or rat, infection occurs. This is 
an important crucial test. 
Rats can become infected when fed on plague cultures or 
on plague cadavers, and the German Commission gave it as 
their opinion that, under natural conditions, rats frequently 
infect themselves by gnawing the infected cadavers of other 
rats, and that they can also become infected through the 
unbroken nasal or conjunctival mucous membrane. Workers 
in India have also been able to infect rats by feeding them 
on plague material or on the cadavers of plague rats. It would 
be natural to conclude that, as the German Commission stated, 
rats in nature often become infected in this manner. But 
this is probably not the case, for the common site in naturally 
infected plague rats of the primary bubo is in the neck, where 
the fleas usually are most numerous ; whereas in experimentally 
infected animals, fed on the afore-mentioned material, buboes 
in the intestinal or mesenteric site are in the great majority. 
Thus out of 5000 post mortems on naturally infected plague 
rats not a single mesenteric bubo was seen. 
Post Mortem Appearances . — Supposing we found a dead rat 
and suspected it of having died of plague. Apart from the 
microscope, what post mortem appearances would we expect 
to find ? Before examining, we would of course take precau- 
tions to rid the animal of fleas, if indeed these had not already 
deserted its cold carcass. 
In dissecting the rat, we would find dark-red, subcutaneous 
injection of the flaps of the abdominal walls. There would 
be fluid in the pleural cavity, haemorrhagic swelling in the 
outer layers of the glands, and swelling of the neck-glands, and, 
in particular, a creamy mottled appearance of the liver. The 
spleen also would be found swollen, congested, and granular 
in appearance. 
Kinds of Bats . — The kinds of rats that concern us mainly 
are those which we might describe as the domestic breed 
as opposed to the field variety. These are Mus rattus , the 
common house-rat, and Mus decumanus, otherwise known as 
