432 MOSQUITOES OF NORTH AMERICA 
the now recognized precautions, as safe almost as they would have been in 
Philadelphia. 
The existence of endemic foci of yellow fever at points in constant communi- 
cation with the Canal Zone, and the consequent danger of reintroduction of the 
disease, has made it necessary to maintain vigorous mosquito control. Aside 
from the comparatively simple control work against house-mosquitoes, a far 
more difficult and extensive campaign has been prosecuted against Anopheles. 
This has proved highly profitable through the resultant reduction in malaria 
and the consequent increased efficiency in the canal workers and saving of 
hospital expenses. The great difficulties imposed by the climate and topography 
of the region in this work against Anopheles were further increased by the opera- 
tions in the construction of the canal which unavoidably created, at least tem- 
porarily, numerous breeding-places for mosquitoes. 
No figures of actual cost of the anti-mosquito work either in Havana or in the 
Panama Canal Zone are accessible to us, but it is safe to say that it was not 
exorbitant and that it was not beyond the means of any well-to-do community 
in tropical regions. 
WORK IN RIO DE JANEIRO. 
One of the most difficult problems of its character was that of freeing Rio de 
Janeiro from its reputation as a great yellow-fever center. The difficulties 
were very great, and the amount of money required for efficient work was 
enormous. Rio de Janeiro has a population of more than 800,000 people; it 
extends over an area of 430 square miles; it is very irregular in its topography, 
varying in altitude from 1 to 460 meters above the sea level; it had at the time 
82,396 houses, and, as in all great centers of population, the inhabitants of many 
of the houses, if not resisting the efforts of the sanitary authorities, surely did 
not facilitate them. 
Work was begun in April, 1903, under the direction of the Public Health 
Service, but the organization effected was of a temporary character and needed 
the passage of new laws by Congress, which were enacted in January, 1904, and 
resulted in the reorganization of the hygienic service of Brazil. A service for the 
stamping out of yellow fever was created. One million six hundred and fifty 
thousand dollars was appropriated annually for this work. The service estab- 
lished included one medical inspector, ten sanitary inspectors (physicians), one 
administrator, one customs inspector, one accountant, seventy medical students, 
nine subchiefs, two hundred overseers, eighteen guards of the first class, eighteen 
guards of the second class, and one thousand workmen; and in addition to this 
personnel, the assistance of the Public Health Service corps of inspectors was 
called upon. 
The city was divided into zones, according to the density of the population, 
and in these zones the work was divided into two sections: (1) Isolation and 
sanitation; (2) the policing of the infected districts. Under the first section, 
yellow-fever patients were removed to the pest house, residents were isolated, 
and houses were disinfected. The second, the sanitary police force, visited every 
