564 The Philippine Journal of Science “gone 
impel us to determine the degree of infection already existing 
in this Archipelago, especially in Samar, by finding the adult 
worms or ova in the vertebrate hosts (man, cat, dog, mice, 
and possibly the carabao), and then to search for the inter- 
mediary host or hosts. 
Should the infection be found endemic in the Philippine Is- 
lands sanitary efforts will be directed, of course, toward the 
hosts, both vertebrate and invertebrate, native and imported. 
Leiper,(20) in investigating the etiology of bilharziasis in 
Egypt, hired small boys to search the pools and canals for 
snails and shellfishes, which were carefully examined in the 
laboratory in order to find the miracidium. Once this was 
found, Leiper was able to trace its life history outside of the 
human body and also the mode of infection. 
To kill all the infected snails Leiper advocates the draining 
of pools and canals. Elgood and Thomas(10) claim that flocks 
of ducks can free the canals from snails. Miyagawa(27) states 
that if lime containing fertilizer (Kalkstickstoff) is scattered 
systematically over a field and its watercourses, all the 
Schistosoma ova and intermediary hosts will be destroyed. 
He observed that all the ova in the stools mixed with urine 
and putrefying material die in two weeks in summer and in 
sixteen days at other seasons. On the other hand, Cort found 
that it is hard to kill snails by chemicals, for they escape from 
water in which there is no food or which has become unsui- 
table for them, and that draining the breeding places would 
be effective only if these places were kept dry at least three 
months. 
Lutz’s(23) observation in Brazil, although it refers to Schis- 
tosoma mansoni, is worth noting, for he says that the larve 
could be hatched from ova many days after they had been 
expelled in the feces; that contact with water is required for 
the ova to hatch; and that these prefer to stay on the surface 
of water. He also found that Planorbis divaceus Spix can be 
infected, infection taking place by way of the antenne, and 
that other flat and long snails attract larve through the an- 
tenne, but that the evolution of the parasite is not complete 
in them. He further states that growth is checked by low 
temperature. 
Manson(24) states that cercarie live only forty-eight hours 
after being discharged from the snail, but a snail may remain 
infected over a long period and continue to give off cercarie, 
and these can pass through the ordinary municipal filter bed 
