and  the  Prevention  of  Rot. 
279 
importance  that  the  whole  question  should  be  investigated,  in 
order  that  it  might,  if  possible,  be  discovered  what  were  the 
proper  preventive  measures  to  be  employed.  The  Council  of  the 
Royal  Agricultural  Society  therefore  provided  the  funds  needful 
to  procure  costly  but  indispensable  apparatus  and  material. 
The  investigation  thus  originated  began  in  the  summer  of  1880, 
and  was  brought  to  a successful  close  in  the  autumn  of  1882. 
What  was  really  known  in  1880  came  very  briefly  to  the 
following.  The  liver-rot  was  a parasitic  disease  due  to  the 
presence  in  the  bile-ducts  of  the  livers  of  the  diseased  animals 
of  great  numbers  of  liver-flukes.  Animals  were  liable  to  con- 
tract the  rot  when  allowed  to  graze  on  low-lying,  wet,  or  ill- 
drained  lands,  and  especially  on  ground  subject  to  floods. 
So  much  Avas  clearly  proved.  In  addition,  it  was  believed  by 
men  of  science,  from  what  was  known  of  the  animals  most 
nearly  related  to  the  liver-fluke,  that  there  rvere  larval  forms 
inhabiting  some  snail  or  slug,  and  that  the  larvae  Avere  subse- 
quently taken  up  by  the  sheep  Avhen  grazing.  Some  had 
suggested  water-snails,  others  land-snails  or  slugs,  and  nu- 
merous attempts  to  solve  the  question  had  been  made  by 
various  eminent  zoologists  ; but  all  had  proved  fruitless,  and, 
notwithstanding  its  great  practical  importance,  the  problem 
remained  unsolved. 
Noav,  however,  the  mystery  has  been  cleared  up,  and  I Avill 
proceed  to  explain  it  in  order,  step  by  step,  so  that  I may 
aftenvards  shoAV  how  and  Avhere  preventive  measures  are  to  be 
applied. 
Part  II. — The  Life-History  of  the  Liver-Fluke. 
Before  giving  the  life-history  of  the  IRer-fluke,  it  will  be  Avell 
for  me  to  explain  a Avonderful  peculiarity  in  the  manner  of  the 
multiplication  and  spread  of  the  animals  belonging  to  the  group 
of  Flat  Avorms  of  Avhich  the  IRer-fluke  is  a member.  The  fully 
groAvn  adults  live  as  parasites  in  some  kind  or  other  of  back- 
boned animal,  such  as  a sheep,  and  there  multiply  by  producing 
eggs.  Each  of  the  eggs  gh'es  rise  to  an  animal,  Avhich  is  neA'er 
like  its  parent,  never  does  become  like  it,  and  never  lives  Avhere 
its  parent  lives.  It  enters  some  snail  or  slug,  and  there  grows 
and  multiplies,  not  in  the  common  way  by  producing  eggs,  but  by 
giving  rise  to  germs  Avithin  itself.  Calling  the  animal  Avhich  is 
hatched  out  of  the  egg  the  first  generation,  these  germs  Avill 
form  the  second.  There  may  be  a third  and  a fourth,  or  even 
more  generations  in  the  snails,  all  these  arising  in  the  same 
Avay  as  germs  ; but  at  length  a form  arises  Avhich  is  destined  to 
leave  the  snail  in  some  Avay  or  other,  to  be  sAvallowed  by  the 
