THE PRESIDENTIAL ADDRESS. 23 
After the long, exhausting Napoleonic wars, with the resulting poverty 
and destitution, typhus fever was prevalent in Great Britain and Ireland. 
About the middle of the century the improved economic conditions 
gradually led to the disappearance of the disease in Britain, although 
cases still occur in some parts of Ireland. 
It is to Nicolle that we owe the advancement in our knowledge of this 
important disease. His work in Tunis on this subject dates from 1909. 
He showed that the blood of typhus cases is infective to monkeys, and, most 
important of all, that the infection takes place through the body louse. 
Just as in trench fever, the louse becomes infective after some five days, and 
it has been shown by the late Arthur Bacot of the Lister Institute that 
the excreta is also infective. 
The minute bodies found in the typhus louse are, subject to some 
differences, very similar to those found in the trench-fever louse and have 
been named Rickettsia prowazeki by Rocha Lima. What group these 
bodies belong to is still a matter of discussion. Some consider them to 
be protozoa, with an ultra-microscopical stage in man and a developmental 
stage in the louse, while others look on them as minute forms of bacteria. 
Although there is still some doubt as to the pathological significance 
of these Rickettsia bodies, the work of Sargent, Rocha Lima, Arkwright 
and Bacot, Wolbach, Todd and Palfrey has done much to establish a 
causal relationship between them and these two diseases, typhus and 
trench fever. 
From the point of view of prevention, the important fact is that the 
infection is carried by the louse, and in the next great war it will be almost 
as necessary to prepare means for the destruction of the lice as of the 
enemy. 
Rocky Mountain Fever. 
A third disease belonging to this interesting little group—Rocky 
Mountain fever—occurs in certain localities in the United States. It 
provides another instance of a virus transmitted by an invertebrate host 
toman. As the result of the work of Ricketts and of Wolbach the wood- 
tick, Dermocentor venustus, is now recognised as the vector. Rickettsia 
bodies closely resembling those found in association with typhus and 
trench-fever virus have been shown to be present in the stomach and 
tissues of the tick, and the same bodies have also been demonstrated in the 
tissues of infected guinea-pigs. 
Another interesting disease of the undetermined group is sand-fly 
fever, the virus of which is conveyed from man to man by the sand-fly. A 
