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EXPEEIMENTAL INFESTATION OF FRESH- WATEE SNAILS. 
By F. G. Cawstoi^. 
A relatively small number of fresh-water snails kept under artificial 
conditions do not thrive well for any lenjj^th of time. Their development 
would seem to depend on warmth, sunlight, and the supply of appropriate 
food. Water-cress is very useful for the supply of the minute organisms 
on which snails feed. 
On several occasions I have secured the adult Schistosomes from animals 
supplied with cercariae developing in Physo2)sis africana in some of the 
rivers and stagnant pools of Natal. I have also secured Fasciola gigantica 
from a guinea-pig which had eaten the encysted cercariae I had obtained 
from Limnaea natalensis in a pool at Sydenham, in the Durban suburbs. 
I was therefore interested to determine whether I could obtain the same 
cercariae in specimens of these two fresh -water snails which had been bred 
from eggs and kept free from all possible sources of infestation except 
from the eggs of Schistosoma haeinatohium and Fasciola gigantic mn. 
In some instances I obtained the eggs of Limnaea natalensis and other 
fresh-water snails from wild water-lilies. But I usually obtained the eggs 
from a jar of water in which I had placed adult snails, so that I could be 
sure of the date on which they were laid, and determine how fast the various 
species developed under artificial conditions. I found that during the 
fourth month the various species had developed sufficiently to be exposed 
to possible infestation. 
On January 7, 1920, I placed 60 Limnaea natalensis which I had bred 
from eggs and kept free from all sources of infection in a jar of water 
containing fasciola from a sheep's liver. The snails were allowed to crawl 
over the flukes, and possibly devour their eggs for most of the day. On 
January 15, eight days later, all were dead. 
On January 16, 30 Limnaea natalensis, also bred from eggs and kept 
free from infection, were placed in a jar of water containing 3 Fasciola 
hepatica and their typical ova from a sheep's liver. 
On January 24, only eight days later, an immature cercaria with a 
relatively large head and slender tail was seen amongst the eggs of one of 
these Limnaeae ; many other cercariae without tails were also seen in a 
young sporocyst in the liver-substance of the snail. This was the only 
