Volume s1-28, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



This investigation was conducted in order to obtain greater numbers of naturally shed cercariae for use in the laboratory of the Commission on Schistosomiasis in the Philippine Islands. The observations and experiments performed provided the following observations:

  • 1.  Alkaline water (optimum pH 7.6) was a critical factor in the natural release of cercariae of from the molluscan host, on Leyte.
  • 2.  Temperature variations of the water, between 19° and 30°C., did not influence the release of cercariae from the naturally infected host, .
  • 3.  Artificial illumination and darkness were similarly unimportant factors; however the natural release of cercariae is of a definite nocturnal periodic nature. Cercariae were released in significant quantities throughout the early evening and continued emerging after midnight, with the peak of production occurring from 9:00 to 11:00 p.m., steadly decreasing as daylight approaches.
  • 4.  Naturally infected will liberate cercariae on two to three successive nights, and then an equally long period will pass before any considerable number of cercariae will emerge. Not a single known positive under observation for 30 days discharged cercariae consistently for more than three consecutive days, thus indicating that the natural emergency of cercariae from this molluscan host is of a cyclic nature.


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