746 THE POPULAR SCIENCE MONTHLY. 



the snails after nursing the young flukes through three generations 

 distribute the tadpole cercarice, which convey the infection back to 

 the sheep, and it there inhabits the liver and causes the disease. 



The Prevention of the Rot. Now that the life-history of the 

 fluke is known, it is not difficult to comprehend the conditions neces- 

 sary for its existence. There must be : (1) Fluke-eggs on the ground ; 

 (2) wet ground or water during warm weather (3) the snail Lim- 

 nceus truncatulus (?) ; and (4) sheep allowed to feed upon the infested 

 ground. 



Under the first condition it may be said that wherever fluked sheep 

 are kept we shall have fluke-eggs. In some districts flukes are always 

 to be found, and where the conditions are the most favorable a sudden 

 outbreak may be expected. The disease sometimes appears in quar- 

 ters where it was previously unknown, and may have been introduced 

 in manure containing fluke-eggs, or adhering to the feet of cattle, dogs, 

 or men. The eggs and young flukes (embryos) may be conveyed by 

 running streams, floods, etc. Other animals than sheep are infested 

 with the parasite, and rabbits and hares may be the means of intro- 

 ducing the plague. The production of the fluke-eggs may be pre- 

 vented by killing the sheep so soon as they are found suffering from 

 the " rot." If there is a suspicion that a flock is attacked, one of the 

 members exhibiting the strongest signs may be killed and its liver ex- 

 amined. If rotted sheep are kept, they should be on dry ground, 

 where the fluke-eggs can not fall on wet land, or be swept into brooks 

 by the descending rains. The manure of infested sheep should not be 

 placed on wet land, and the livers of rotted sheep ought to be de- 

 stroyed or deeply buried. 



The remedy for the second condition is a simple one, but not always 

 easy of application. Wet land should be thoroughly drained, and, 

 besides preventing the rot, it will greatly improve the pasturage. 

 When draining can not be done, lime or salt may be scattered over 

 the surface. These substances will destroy the embryos, the more 

 developed encysted form of the fluke, and the snails which serve as 

 hosts. The salt or lime should be applied in early summer, when the 

 young flukes are present in the greatest numbers. 



There seems to be only one snail in England which is host to the 

 young flukes, and the accounts of Professor Thomas in exposing other 

 species of Limnwus to the embryos of the fluke are most interesting. 

 The Limnceus truncatulus (Fig. 5) is said not to exist in the United 

 States, though several other kinds of snails belonging to the same 

 large genus are found here. It is probable that with us some other 

 species than Limnceus truncatulus serves as the host of the intermedi- 

 ate forms of our liver-flukes. Draining the wet land will reduce the 

 number of snails ; and dressings of lime or salt, as above mentioned, 

 also destroy them. The lime should be scattered especially on or 

 near marshy places and along ditches. If a pasture has been flooded, 



