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_.

If he finds a snail, he bores his way into its flesh and soon begins to grow and wax fat.