lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



direct sunlight continued to develop. Brown (1927) exposed the eggs 

 of A. lumhricoides to direct sunlight in Panama by placing them in 

 sand, and after a period of 21 days of such exposure it was found that 

 all of the ova had degenerated. Brown considered that the destruction 

 of the ova was due to two factors, viz, high temperature and desic- 

 cation. Soil temperatures in the sand cultures were found to reach at 

 least 123° F., which appears to be above the lethal range of heat for 

 ova of this species. Caldwell and Caldwell (1928) exposed fecal-soil 

 cultures of the ova of the human and pig ascarids to sunlight in Ala- 

 bama, and after a period of 3 days' exposure, the ova in all cultures 

 were disintegrated. The maximum temperature recorded in the cul- 

 tures was 146° F. These investigators place great emphasis on 

 desiccation as the chief lethal factor involved, inasmuch as cultures 

 moistened at hourly intervals while exposed to sunlight showed little 

 disintegration of the ova of the pig ascarid; ova of the human ascarid 

 showed less resistance. Otto (1929) reported that eggs of the human 

 ascarid developed and remained alive over the summer of 1928 on the 

 surface of clay, loam, sand, and cinder-loam soils in the shade in south- 

 western Virginia. Many of the eggs on the first three soils in the sun 

 died rapidly, but after 160 days about one-fourth of the eggs isolated 

 were still alive, whereas most of those on cinders in the sun died before 

 becoming embryonated. The high temperatures recorded on the surface 

 of the cinders lead the author to conclude that temperature played an 

 important part in the death of these eggs. 



Apparently, Owen (1930) is the only investigator to observe the 

 effect of sunlight on the ova of Toxocara canis. Owen exposed the ova 

 of this species to summer sunlight in Kentucky and Minnesota and 

 found that such ova disintegrated before reaching the infective stage. 

 A surface-soil temperature of 131.9° F. was obtained on the plots of 

 soil on which the eggs were exposed. Owen was of the opinion that 

 the failure of the eggs to develop was due to the high temperature. 



Schwartz (1932) reported that ova of Ascaris vitulorimi did not 

 survive exposure on glass slides to i hour's direct sunlight in the 

 Philippines. Eggs exposed in beakers of water also failed to survive 

 after i hour of direct sunlight. Schwartz then exposed ova in vials 

 painted with India ink to exclude light. An exposure of i hour in 

 sunlight was lethal to ova in painted and unpainted vials, and Schwartz 

 thus attributed the death of the ova to the temperature, which reached 

 45° C. 



Ohba's negative results from exposure of ascarid ova to sunlight 

 are difficult to interpret in the light of our irradiation tests, as the 

 length of exposure is not stated in the English summary of Ohba's 



