THE PRESIDENTIAL ADDRESS. 19 
One of the best examples of the prevention of disease is the attack 
made on yellow fever in Rio de Janeiro, the capital of Brazil, by the 
well-known scientist, Dr. Oswaldo Cruz, with the result that the annual 
deaths in the city from yellow fever fell from 984 in 1902 to O in 1909. 
This brilliant result was brought about by the destruction of the 
_ Stegomyia mosquito, the intermediate insect host in yellow fever. 
So also in the case of malaria. A dozen years ago, based on the 
experience gained by Ross on the West Coast of Africa and Ismailia and 
by Watson in the Federated Malay States, the method of prevention by 
mosquito control and drainage has been so perfected that the practical 
blotting out of malaria from a given locality is now merely a matter of 
expense. A great deal of work has been done during the last few years 
in the way of experiment in the United States, and Vincent, the President 
of the Rockefeller Foundation, lately stated that there is evidence that 
“under normal conditions an average community can practically rid itself 
of malaria at a per capita cost of from 45 cents to $1 per year.’ 
This is an altogether inadequate account of the methods of preventing 
these highly important protozoal diseases. From the few examples given, 
it will be seen that they are most rampant in warm climates, that they 
are as a rule conveyed from the sick to the healthy by an insect interme- 
diary, and that it is by an attack on this insect, be it mosquito, tsetse-fly, 
or tick, that the best chance of success in prevention lies. 
, INFECTIOUS DISEASES.—(C) UNDETERMINED GROUP. 
In addition to the bacterial and protozoal infectious diseases, there is a 
third and large class, known as the ‘ undetermined group,’ in which the 
parasite is either unknown or doubtful. Many of these undetermined 
diseases are very common and familiar, such as influenza, measles, scarlet 
fever, smallpox, typhus fever, trench fever, dengue fever, and sand-fly 
_ fever; among animals, rabies, rinderpest, foot-and-mouth disease, and 
African horse-sickness. 
The theory generally held at present in regard to most diseases included 
in this group is that the living germs causing them are ultra-microscopical, 
in at least some part of their life history, and this is strengthened by the 
- fact that many of them pass through porcelain filters, which keep back the 
smallest of the visible bacteria. Hence the name, ‘ filter-passers.’ 
Many of these undetermined diseases are highly infectious and appear 
to infect at a distance through the air, as, for example, in influenza, 
scarlet fever, and smallpox. 
