THEIR CAUSES, NATURE, AND PREVENTION. 195 



very wide experience, I have never yet met with any outbreak 

 of lung disease in sheep the characters and cause of which 

 warranted me in attributing to it, even in the slightest degree, 

 contagious properties. I have been able to trace all such cases as 

 have come under my notice to purely local causes — to, in fact, 

 improper management in the way of feeding associated with ex- 

 posure to cold and wet and to rapid alternations of temperature. 



In many instances the foundation for lung disease is laid at 

 birth, the lungs, owing to the lowering influence of cold or cold 

 and wet, never being properly inflated. Lung disease of this 

 class is more prevalent in some districts than others and parti- 

 cularly in exposed localities ; and this fact points to the necessity 

 of providing sheep, when possible, with artificial shelter in bad 

 weather. 



The animal parasites of most importance to breeders of 

 sheep are those associated with rot, with sturdy and with hoose. 

 Tape-worms and round worms in the intestines are also some- 

 times the cause of great losses. 



Mot is due to a flat worm known as the fluke (Distoma 

 hepaticimi or Fasciola hepaticumi), which inhabits the bile ducts 

 of the liver and there sets up extensive inflammation from 

 which result various organic changes, such as hardening and 

 softening, leading in the end to annihilation of its function 

 and, as a result, emaciation, anaemia, dropsy, diarrhoea, and 

 death from exhaustion: in cold nights following warm days 

 numbers die from congestion of the lungs as the result of chill. 



A few of the more important features only of the worm and 

 its life history can be here alluded to. 



The worm itself is bisexual (hermaphrodite) and is pro- 

 pagated by eggs which are passed out with the bile and the 

 dung in countless thousands and lodge upon the grass or other 

 places. If the eggs fall on to dry soil, no harm results ; if, on 

 the contrary, they fall on wet places the disease is propagated 

 to other sheep. 



The Qgg is oval in shape, has a lid (operculum) at one ex- 

 tremity and contains an embryo which, when fully matured, is 

 provided with delicate hair-like processes known as cilia. The 

 lid of the egg-shell, partly by the agency of moisture, partly by 

 the movement of the contained embryo, is lifted and allows of 

 the escape of the latter when it at once begins to move actively 

 about in search of a host in the form of a particular snail (the 

 Limnus triincatulus), whose body it penetrates by the aid of a 

 boring apparatus and there becomes encysted and during its resi- 

 dence therein it undergoes a series of wonderful changes in form, 

 passing through several generations, until a tadpole like crea- 

 ture is produced, which after gaining its liberty encysts itself 

 at the lower parts of the blades of grasses from whence sheep 



