240 The Philippine Journal of Science 1915 
larvicide in mechanically in order to destroy the larve of these 
stream-breeding species, especially where much vegetation is 
present. In the walled ditches passing under houses or into 
other inaccessible places a simpler treatment might be devised. 
As stated above, Anopheles febrifer and other stream breeders 
avoid rice paddies and water in ditches which has previously 
stood on large paddies. Moreover towns in rice-paddy regions 
where there are few brooks or other streams are comparatively 
malaria free. In Calamba, Laguna Province, a ditch from a rice 
paddy flows through the main street of the town, and laterals 
extend to other streets. We could find no anopheles other than 
A. rossu in this ditch, and the malarial index of the children of 
the town is 0. 
Watson?! remarks on the fewness of stream breeders and 
the comparative absence of malaria in certain rice-paddy areas 
in the Federated Malay States while malaria is plentiful in the 
neighboring hill regions. He believes that irrigation as well as 
drainage may in some localities be an efficient antimalarial 
measure. : 
Kendrick”? finds that in the irrigated rice regions of central 
India two factors must coexist in order to bring about a high 
rate of endemic malaria: namely, breeding places of anopheles- 
mosquito carriers and shade in the form of trees, shrubs, long 
grass, or other jungle. 
Not all the species of malaria-bearing anopheles of central 
India are found in the Philippines. Climate and other con- 
ditions differ so that we do not expect the distribution of malaria 
here to correspond closely with that of India, but it is worthy 
of note that in the Philippines as well as in central India open 
irrigated rice regions may be nearly malaria free. Generally 
malarious localities in the Philippines are on streams which come 
more or less directly from wild land or land uncultivated for 
many years. In some parts of the Philippines the further 
development of rice culture may result in the diminution of 
malaria. However, water in irrigation ditches, if it has not 
previously stood on extensive rice paddies, affords good breeding 
places for Anopheles febrifer. 
While drainage has undoubtedly played a large part in the 
diminution of malaria in various regions—for instance, the 
middle west of the United States—it seems that extensive cul- 
tivation of the soil might also have been an important factor. 
** Loe. eit. 
* Ind. Journ. Med. Res. (1914), 4, suppl. 64. 
