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The tributary streamlet meanders through a succession of pasture
meadows, in one of which the beds themselves are situated, and here
throughout most of the year the fleecy victims of the human carnivore
carry on the industry of converting grass into mutton. Now it happened
some years ago that the sheep frequenting these pastures became affected
with the disease known as 'liver-rot'; and here we must make a short
digression into the domain of pathology.
"'Liver-rot' is a disease of quite romantic antecedents. Its cause is a
small, flat worm--the liver-fluke--which infests the liver and
bile-ducts of the affected sheep.
"Now how does the worm get into the sheep's liver? That is where the
romance comes in. Let us see.
"The cycle of transformations begins with the deposit of the eggs of the
fluke in some shallow stream or ditch running through pasture lands. Now
each egg has a sort of lid, which presently opens and lets out a
minute, hairy creature who swims away in search of a particular kind of
water-snail--the kind called by naturalists _Limnaea truncatula_.


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