sheep diseases: causes, nature and prevention. 355 
Rot is due to a flat worm known as the fluke (. Distoma 
liepaticum or Fasciola hepaticum), 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 exhaus¬ 
tion ; in cold nights following warm days numbers die from con¬ 
gestion 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 propagated 
by eggs which are passed out with the bile and the dung in count¬ 
less 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 egg is oval in shape, has a lid (operculum) at one ex¬ 
tremity aud 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 truncatulus) y 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 creature 
is produced, which after gaining its liberty encysts itself at the 
lower parts of the blades of glasses from whence sheep pick it up 
in the process of grazing; ultimately it finds its way into the 
liver. 
Sheep are more susceptible to rot than are other animals, 
simply because they bite closer—a hog-mouthed sheep escapes; 
but cattle, and very many of them too, and occasionally in wet 
seasons colts also, suffer from the ravages of the fluke. 
Hot is never seen on dry lands nor on salt marshes, and even 
rotting grounds are safe after a frost. 
The lessons to be learned in reference to rot are—1st, that it 
