304  The  Natural  History  of  the  Liver-iluhe 
The  half  fed  with  corn  and  salt  were  quite  sound  ; the  other 
half  had  flukes  in  their  livers,  so  that  they  could  not  have  been 
kept  through  another  winter.  Mr.  Heath  had  no  cause  of 
complaint  with  his  speculation,  as  the  subject  of  his  experiment 
realised  a profit  of  about  50s.  per  head,  and  the  cost  of  corn  and 
salt  did  not  exceed  3s.  each. 
Sheep  must  not  be  allowed  to  graze  too  closely,  for  they  are 
then  specially  liable  to  take  the  rot.  Not  only  does  close- 
grazing imply  that  food  is  scanty,  and  that  the  health,  and 
therefore  the  digestive  power,  of  the  sheep  is  likely  to  suffer  in 
consequence,  but  the  sheep  will  pick  up  more  fluke-germs. 
The  snail,  in  crawling  about  in  the  grass,  keeps,  as  a rule,  at 
the  bottom,  close  to  the  roots  ; the  cercariae  accordingly,  on 
leaving  the  snail  and  proceeding  to  form  their  cysts  or  envelopes, 
will  attach  themselves  to  the  stalks  of  grass  or  other  plants,  close 
to  the  ground.  Hence  the  closer  the  sheep  grazes,  the  more  of 
these  cysts  it  is  likely  to  pick  up.  There  are  many  instances 
on  record,  and  I have  myself  met  with  others,  in  which  “ hog- 
jawed”  sheep,  which  are  unable  to  graze  closely,  have  escaped 
infection  when  all  the  rest  of  the  flock  have  been  rotted.  The 
special  liability  of  sheep  to  the  fluke  seems  in  some  measure  to 
be  due  to  the  fact  that  it  can  graze  more  closely  than  any  other 
domestic  animal. 
Summary  of  Preventive  Measures. — I may  now  give  a summary 
of  the  preventive  measures  which  have  been  suggested  above. 
1.  All  eggs  of  the  liver-fluke  must  be  rigorously  destroyed  ; 
manure  of  rotten  sheep,  or  other  rotten  animal,  must  not  be  put 
on  wet  ground. 
2.  If  sheep  are  rotten,  let  them  be  sent  to  the  butcher  at  once, 
unless  they  are  specially  valuable  and  are  not  badly  fluked.  If 
kept,  they  must  not  be  put  on  to  wet  ground. 
3.  Care  must  be  taken  to  avoid  introducing  eggs  of  the  fluke, 
either  with  manure,  or  with  fluked  sheep,  or  in  any  other  way. 
Rabbits  and  hares  must  not  be  allowed  to  introduce  the  eggs. 
4.  All  heavy  or  wet  ground  must  be  thoroughly  drained. 
5.  Dressings  of  lime  or  salt  should  be  spread  over  the  ground 
at  the  proper  seasons  to  destroy  the  embryos,  the  cysts  of  the 
fluke,  and  also  the  snail  which  acts  as  host. 
6.  Sheep  must  not  be  allowed  to  graze  closely,  for  the  more 
closely  they  graze,  the  more  fluke-germs  will  they  pick  up. 
7.  When  sheep  are  allowed  to  graze  on  dangerous  ground, 
they  should  have  a daily  allowance  of  salt,  and  a little  dry  food. 
If  all  farmers  will  unite  in  carrying  out  the  above  preventive 
measures,  suggested  by  the  knowledge  of  the  life-history  of  the 
parasite,  there  is  no  reason  why  the  fatal  ravages  of  the  de- 
