Prevention and Eradication 



81 



Beta-naphthol 



Thymol .. 



Fresh chlorinated lime 



Sodium hydroxide 

 Chloroform water 



Effect of 



Temperature 



ON Meta- 



MOKPHOSIS. 



Cresol . . . . . . 1 ill 10,000 . . All dead in 5 minutes. 



Microcidine . . . . 1 in 10,000 . . All dead in 20 minutes. 



Dead in 50 minutes. 



Dead in 2 hours 50 minutes. 



Kills immediately. 



Stopped swimming immediately. 



Fibrillar twitching and wriggling in 

 1^ hours ; motionless in 2 hours. 



Swimming stopped in 1 hour ; quite 

 motionless in 2 hours. 



Dead in 30 minutes. 



Slight contraction at 50 minutes ; 

 dead in 3^ hours. 



Kills immediately. 



All movement stopped in ^ hour ; 

 dead in ^ hour. 



Swimming stopped in 2 minutes ; 

 some creeping. 



Body disintegrated in 1 hour. 



Kills at once. 



Dead in 3 minutes. 



Actively swimming after 1^ hours. 



Active after 2| hours. 



Immediate immobilization. 



Actively swimming after 2 hours. 



Paralyzes swimming ; ineffective creep- 

 ing movements. On addition of water 

 swimming regained in 5 minutes. 



Many treinatodes undergo their larval meta- 

 morphosis in molluscs during certain months of 

 the year. Looss [290] remarked that in Egypt 

 when the temperature falls in winter to about 

 5^^ to 6° C. the growth and multiplication of larval trematodes is 

 sometimes wholly suspended, while in Central Europe it is only 

 retarded at this temperature. Autumn seemed to be the most 

 favourable period for fresh infections of intermediate hosts. During 

 winter young parasites develop little by little but only reach the 

 stage of cercarial production in the warm season. The appended 

 table shows the monthly variations in the temperature of water 

 near Cairo. 



During February we found sporocysts containing secondary 

 sporocysts and bifid-tailed cercarise in Planorhis mareoticus. In 

 March eyed bilharzia cercariae were found also in this species. 

 Non-eyed bilharzia cercariae were first detected in P. hoissyi on 

 April 17 and in Bidlinus on June 8. Once located, the cercariae 

 were obtainable throughout the entire year, but were very scarce 

 from January to March. In would appear, therefore, that 

 infection is by no means confined to the autumn as has been 

 generally supposed. 



Free swimming cercariae could not be recovered 

 from infected waters, as they pass through the 

 finest silk mesh. They readily pass through stocking material, and, 

 6 



Penetration. 



