264 
Liver Rot of Sheep 
(c) Those snails not giving off cercariae almost always outlived the 
specimens that were infected, which generally died. 
(. d ) The majority of cercariae appear during the first day of an 
experiment and thence decrease in numbers. 
This result may be due in some way to the waning vitality of the host. 
Cercariae when extended and creeping by means of the ventral 
sucker usually measure 0-75 mm. in length (total). They swim with 
great vigour for a length of time varying (in my experience) with the 
vitality of their host; those from moribund snails either fall to the 
bottom, become encysted upon the walls of the vessel or lose their 
tails (and float in that condition) within 24 hours; while cercariae 
from active, healthy snails may continue to swim for some days. In 
one case some were still active on the 5th day after leaving the host. 
In all cases great care was taken that no fresh cercariae could have 
become mixed with those obtained each day. 
While testing the vitality of L. truncatula dried both naturally and 
artificially, an interesting fact came to light. If infected snails that have 
been out of water for several days are re-placed in it, numbers of 
cercariae will frequently appear, almost at once, even should the snail 
be moribund. While experimenting to discover the food, etc., of 
truncatula a number of infected specimens were placed on a sod and 
immersed to the depth of an inch. Several of these crawled up stems 
of grass for about 1| inches and there affixed themselves as usual under 
drought conditions. Two days later, wishing to test the effect of dew 
and rain shower upon such individuals I damped these until drops of 
water hung from or surrounded them. The snails did not move, but 
upon examining with a hand lens five minutes later the drops were seen to 
be full of active cercariae. The question arises then, would it be possible 
for a sheep to become infected directly by eating such a blade of grass, 
snail and all? It is also possible for animals to obtain from a pool or 
trough many living cercariae and others that float after having cast 
their tails. Despite repeated attempts I have never induced cercariae 
to encysts upon grass, they always settled and encysted upon the glass 
sides or bottom of the tube or dish. 
An endeavour to ascertain the effects of cercariae upon the snails 
was made at my suggestion by Miss 0. M. Rees, M.Sc., in 1915. Sections 
were cut of snails that had produced cercariae after capture and also 
of others not infected. The only conclusion arrived at was that, while 
difference were observable in the structure of the livers of the infected 
snails, yet no rediae or cercariae were recognisable. 
