Rae, 8 Barber et al.: Malaria in the Philippines 992 
similar test of children of 5 years of age or under would prob- 
ably give higher percentages of positives (Table VI, No. 10, 
Magdalena) . 
The “ditch” or ‘canal’ towns have a peculiar interest on 
account of their topography and may well be considered apart. 
Water, which is usually obtained from a neighboring brook or 
river, is brought into one of these towns by a large ditch or canal. 
In the town many laterals carry the water to various streets, 
where it is available for laundry or culinary purposes, and 
smaller laterals carry it between and under houses for the pur- 
pose of carrying away sewage. The water is usually clear, and 
may flow swiftly or quietly through the ditches, depending on 
the nature of the town site. Small dams are frequently made 
in order to obtain a convenient source of water for laundry or 
other purposes. The ditches are sometimes walled, usually with 
loose stones, but often have only the natural clay sides. Grass 
frequently grows at the margin, and various refuse finds its way 
into the water. As numerous examinations have shown, these 
ditches are excellent breeding places for Anopheles febrifer. We 
have found this species abundantly at the grassy margins of 
the ditches and occasionally in crannies of the walled sides. 
Few other mosquitoes have been found in these ditches. Fre- 
quently where the water is very swift in the street ditches small 
laterals, often immediately under the houses, furnish favorable 
breeding places. 
For convenience the “ditch” towns are taken from Table VI 
and given in a separate table with additional data (Table VIII). 
TABLE VIII.—‘“‘Ditch” or “canal” towns. 








No. 
eae Name. | General surroundings. Ditches. geese 
Vi. 
25 Calambase = 2 e_ | Level plain; irrigated | One main; several laterals; | River, side of 
rice country. flow comparatively slug- town. 
gish. Water from rice 
paddies. , 
OMEN Os omen = oo Hilly region near | Many laterals; clear water, | Brook, side of 
mountains. mostly swift, but some town. 
quiet places. 
10 | Magdalena -______. Plain; coconut-palm | Very many laterals; clear | Brooks, one on 
region. water; flow compara- either side of 
tively slow. Much veg- town. Pools 
etation. near market. 
UGS) WEEN AGA, oe wo Hilly; near moun- | Many laterals; clear water; | Brook in and 
tains; elevation, 275 flow swift with some near town. 
meters. quiet places. Some 
| vegetation. 
