Experimental Tvfestaiion of Fresh-Wafer Siiaih. 
303 
and of spreading infection' in rivers. On March 26 four of these snails 
were dead, but each appeared to harbour sporocysts in their liver-substance. 
On April 12 no cercariae were present in Isidora tropica and Isidora 
forsJcali which had been bred from eggs and exposed to the same miracidia 
on February 21. 
I have demonstrated Bilharzia infection in some 30 distinct Physopses 
four to six weeks after exposing them to the miracidia of 8. haematobium. 
These snails have been bred from eggs, and kept in tubs or jars of water 
removed from all sources of infection other than that due to experimental 
intervention. 
