her the
flea nor the bug, but probably the clothes-louse. Although the smaller
monkeys cannot be directly infected with typhus fever from man, it was
found that (as with some other infections) the bonnet monkey was
susceptible to the infection after it had passed through the
chimpanzee. Experiments were, therefore, made with clothes lice taken
from a healthy man, and kept for eight hours without food. They were
placed on a bonnet monkey which was in full typhus eruption. A day
afterwards they were removed to healthy bonnet monkeys with the
result that the healthy bonnet monkeys developed typhus fever. There
is thus no doubt whatever that typhus fever can be carried in this way
from bonnet monkey to bonnet monkey. The whole history of typhus fever
fits in with the carriage of the infection in the same way from man to
man, and not with the notion of an aerial dispersion of the infection.

The fact that typhus only exists in very dirty and crowded
populations, and that it has disappeared where even a moderate amount
of cleanliness as to person and clothing has become general, coincides
with the possibility of the body louse as carrier. This little
parasite is known to be a wanderer, and is gifted with a very acute
sense of smell. An individual placed in the centre of a glass table
invariably walked, guided by the scent, towards the observer, at
whatever position he placed himself. Sulphurous acid is a violent
repellant of these creatures. Not only will it kill them if they are
exposed to its fumes, but traces of it drive them away. Hence doctors
and nurses who have to handle typhus patients or their clothes have
only to wear a small muslin bag of sulphur under their garments, or to
rub themselves with a little sulphur ointment in order to be perfectly
guarded against infection; the louse will not approach them, nor
remain upon them should it accidentally effect a lodgment.

It is not always obvious at once in what way a knowledge of the mode
of carriage of a deadly disease can be of service to humanity. But in
this case it is strikingly and triumphantly clear. In the vast
poverty-stricken population of Russia typhus is still common. Public
medical officials attend these cases, and the Russian Government keeps
a record of the annual deaths of its medical staff, and of the causes
of their deaths. In the first six months of last year 530 Russian
medical officers died, and twenty-four of these deaths were caused by
typhus fe