302 
The  Natural  History  of  the  Liver-Fluke 
of  the  liver-fluke.  Consequently,  wherever  this  snail  is  absent 
there  can  be  no  liver-rot,  and  if  we  could  succeed  in  extermi- 
nating it,  we  should  render  it  impossible  for  the  disease  to  exist 
in  England. 
Fig.  19. 
The  snail,  Limnceus  trunca- 
tulus , which  serves  as  hust 
to  the  sporocy6t,  redia,  and 
growing  cercaria  of  the 
Liver-fluke.  The  drawing 
is  magnified,  and  the  true 
length  is  shown  by  the  line 
at  its  side.  (Original — 
A.  P.  T.) 
The  snail,  however,  is  small,  and  hence  difficult  of  detection, 
so  that  all  we  can  hope  to  do  is  to  limit  its  numbers  in  any 
given  locality.  There  are  several  ways  in  which  this  may  be 
done.  First  of  all,  the  land  should  be  well  drained.  I have 
known  an  instance  in  which  Limnceus  truncatulus  was  found 
in  a small  boggy  place  towards  the  middle  of  a field,  and  was 
there  the  means  of  propagating  the  fluke.  When,  however,  the 
marshy  place  was  drained,  the  snail  disappeared  from  the  ground, 
and  with  it  the  fluke-disease.  A dressing  of  lime  or  salt  will, 
as  already  mentioned,  destroy  the  snails,  and,  if  applied  to  the 
ground  for  this  purpose,  it  should  be  scattered  especially  on  or 
near  any  marshy  places,  or  along  the  margins  of  ditches,  ponds, 
or  streams,  out  of  which  the  snail  will  naturally  crawl. 
A flood  may  bring  the  snail  down  in  quantities,  and  scatter 
it  broadcast  over  fields  which  were  previously  free  from  it  (see 
p.  292).  The  snails  may  be  infected  before  they  are  brought 
down  by  the  flood,  and  infection  be  thus  introduced  into  new 
areas ; or  they  may  become  infected  subsequently,  if  there  are 
eggs  on  the  ground.  They  are  drifted  everywhere.  Flooded 
land  should  therefore  have  the  salt  or  lime  scattered  over  the 
whole  of  its  surface  when  the  waters  have  gone  down. 
4th  Condition.  Sheep  or  other  animals  must  be  allotvcd  to  feed 
on  the  same  ground , without  proper  precautions  being  taken. — If 
Fig.  20. 
Limnceus  trunca- 
tulus, of  natural 
size.  (A.  P.  T.) 
