44 
Lice and Disease 
should have been considered first, as the investigation of this disease 
by Sergent preceded and stimulated similar researches into the etiology 
of typhus by Nicolle and his collaborators. The latter disease, however, 
is given precedence because of its graver character. The remaining 
subject-matter is similarly treated in the order of its practical im¬ 
portance. 
I. TYPHUS FEVER AND ITS CONVEYANCE BY LICE. 
1. The Geographical Distribution and Prevalence of Typhus. 
Typhus was exceedingly prevalent throughout Europe in former 
times, but, apparently owing to a general improvement that took place 
in hygienic conditions lasting up to the outbreak of the present war, 
the disease had gradually become almost entirely confined to certain 
endemic areas. 
Typhus is essentially a disease of cool and temperate climates. 
In Europe, during recent decades, it had been chiefly recorded from 
Galicia, Poland, European Russia, Ireland, and Italy, all but the last 
having been regarded as its chief endemic centres. Typhus occurred 
to a moderate extent in England, Wales, and Scotland, and to an 
undeterminable degree in Finland, Spain, Portugal, Bohemia, Austria, 
Hungary, Bukowina, Roumania, Bulgaria, Montenegro, Serbia, Greece, 
Turkey, and some of the Mediterranean Islands. The disease had 
grown rare in Norway and Sweden, Denmark, Holland, Belgium, 
France (since 1893), and Switzerland, and this may also be said of 
Germany where the cases that occurred were largely imported from 
Russia and Galicia. On the continent of Africa, it has been recorded 
from the countries bordering upon the Mediterranean (Morocco, Algeria, 
Tunisia, Tripoli, Egypt), where it may be regarded as endemic. In Asia, 
typhus occurs in Asia Minor, Armenia, Persia, Mesopotamia, the Caucasus, 
Siberia, Central Asiatic Russia, India, Northern China, Korea and 
Japan. In America, it is still reported occasionally from Canada and 
the United States where severe epidemics followed on the track of 
Irish immigrants in the middle of the last century; it has, moreover, 
been recorded for a long time from Peru, Chile, Brazil, Bolivia, Nicaragua, 
and it is endemic in and about the City of Mexico 1 . 
The prevalence of typhus in the centres where it occurs most fre¬ 
quently is shown in the following table, the latter requiring but little 
1 These data have been compiled from Hirsch (1881), Clemow (1903), Low (1916) 
and knowledge personally acquired. 
