234 The Philippine Journal of Science 1915 
where a comparatively malaria-free population has been intro- 
duced into a malarious district. Dr. G. W. Daywalt informed 
us that a group of about 400 laborers came to the San Jose 
Estate in February and March, 1911. Within two weeks 90 
per cent of them were attacked by malaria of a pernicious type, 
and many of them died. This was in the dry season. Gen- 
erally, according to Doctor Daywalt, the severest epidemics 
on the San Jose Estate have begun in May, a hot month with 
frequent afternoon showers. 
On the line of construction of the Manila railroad where 
malaria was very prevalent at least up to November, 1914, the 
fewest cases appeared in the hot dry season, according to Dr. 
S. R. Cox, who until recently was resident physician there. 
Barber surveyed this region during the dry season and again 
in November. Evidently there is much more flow of water in 
the brooks, which are plentiful there, after the rainy season, 
and some brooks go dry, or nearly so, in the dry season. La- 
borers were continually being introduced into this region from 
Cebu and other relatively nonmalarious regions. 
The severe epidemic at the bridge-construction camp at Ba- 
liuag River, in Nueva Ecija Province, occurred in the dry sea- 
son—that is, November, December, January, February, and 
March. The epidemic on the line of construction of the Manila 
water works in 1906 occurred in February. 
The severe outbreaks mentioned above have occurred near the 
habitat of stream-breeding mosquitoes and at times when their 
breeding was not interfered with by freshets or drought. In 
the “ditch” towns (Table VIII) the supply of water is often so 
regulated that breeding is less interfered with by heavy rains. 
We found a very high rate of infection in Magdalena, Laguna 
Province, in July, and the people in this town state that the 
fever is worse during the rainy season. 
We believe that the results of our work give a more opti- 
mistic outlook for successful antimalarial work in the Philip- 
pines. Large parts of the more populous portions of the Is- 
lands contain little or no indigenous malaria, and the people 
residing in them are little exposed to infection. It is probable 
that the amount of morbidity and mortality from malaria in 
the Philippines has been overestimated. The following data 
were kindly furnished us by Dr. Victor G. Heiser, Director of 
the Bureau of Health of the Philippine Islands: 
