LIVER ROT, COATHE OR BANE. 22Q 



The liver fluke follows this dual existence, and at different 

 stages is found inhabiting the body of a mollusc, shown by 

 Thomas to be the Lymnaus tvuncatulatus, a freshwater snail with 

 a brown spiral shell, which is very common and widely dis- 

 tributed, but has no popular name. The late John Henry 

 Steel informs us in his excellent treatise on " Diseases of the 

 Sheep " that its shell is sometimes under a quarter of an inch, 

 and never over half an inch, in length, and Thomas found that 

 these snails suffer much from the invasion of the fluke in a 

 certain stage of their existence, and that this fluke disease is 

 as fatal to them as to the sheep. The invasion takes place, so 

 far as the snails are concerned, in \pril and May, but more 

 generally in June and July. " A severe winter kills off * rotten 

 snails,' but a mild winter may simply render them torpid, and 

 thus unusually early cases of rot in sheep may occur in the 

 following May. In the tissues of this snail it develops into the 

 sporo-cyst, redia, or * nurse,' a kind of sac in which develop 

 numerous larvae with tails (cercariae). These escape through 

 a special vent in the redia, and for a time lead independent 

 free lives in water. They then come to rest, cast their tails, 

 and develop an enveloping cyst of a snow-white colour which 

 adheres to the stalks or leaves of grasses and water plants. 

 These may remain a few weeks, but if they undergo no further 

 change of conditions the embryo within perishes. In this form 

 on grass or in water they pass into the alimentary canal of the 

 host or ultimate bearer (sheep, horse or other mammal), and the 

 pupa-cyst is digested by the action of the gastric juice, and 

 from the stomach of the host through the duodenum and bile 

 duct the fluke passes gradually up to the liver." Whether 

 this is an absolutely correct account of the development of 

 the fluke may be doubted, as Cobbold remarks that *' there is 

 no recognisable limit to the variety or to the extent of larval 

 fluke development." To speak generally, there appears to be 

 no doubt that by some such process as that described the 

 fluke passes from the snail into the digestive system of the 

 sheep, and from thence into the bile ducts, where it arrives at 

 the stage of sexual development or maturity. 



