40 
Tuberculosis. 
eradicate  the  disease.  A second  test  of  such  animals  after  a 
short  interval  is  necessary,  because  at  the  time  of  the  first 
test  some  of  them  may  have  been  so  recently  infected  that 
tuberculin  will  not  yet  provoke  a reaction  in  them.  In 
animals  experimentally  infected  it  has  been  found  that  a 
reaction  may  not  be  obtainable  until  seven  weeks  afterwards, 
and  it  is  possible  that  in  cases  of  natural  infection  the  interval 
is  sometimes  longer.  Having  regard  to  this  fact,  it  is  probably 
best  to  carry  out  the  second  test  three  months  after  the  first, 
and  it  certainly  should  not  be  delayed  beyond  that. 
The  three  measures  that  have  just  been  prescribed — initial 
test,  separation  of  the  non-reacting  from  the  reacting,  and 
re-testing  of  the  non-reacting  animals  within  three  months — 
are  the  only  ones  that  must  be  universally  applied  ; the  further 
steps  for  eradication  of  the  disease  may  be  modified  according 
to  the  circumstances,  and  several  possible  cases  may  be 
separately  considered. 
The  ease  or  difficulty  of  eradication  depends  mainly  on  the 
proportion  of  animals  reacting  to  the  first  test  and  their  value. 
The  most  favourable  case  is  that  in  which  the  number  of 
reacting  animals  forms  only  a small  proportion  of  the  entire 
herd  and  the  individual  value  of  these  animals  is  not  very 
great.  Unfortunately  there  is  reason  to  fear  that  in  herds  of 
any  size  it  is  a rare  case.  In  many  herds  in  which  the  calves 
are  separated  from  the  cows  at  birth,  and  are  afterwards  kept 
apart  from  these  while  indoors,  the  proportion  of  reactions  in 
the  young  stock  (under  two  years  old)  is  often  small,  but  if 
any  disease  at  all  exists  in  the  herd  anything  between  20  and 
80  per  cent,  of  the  breeding  animals  may  react.  When  the 
proportion  is  less  than  20  per  cent.,  and  indeed,  whenever  the 
owner  feels  that  he  can  stand  the  initial  sacrifice,  it  is  best 
to  dispose  of  the  whole  of  the  reacting  animals  immediately 
or  as  soon  as  they  can  be  made  ready  for  the  butcher,  the  fact 
that  they  are  reacting  animals  being,  of  course,  disclosed  to 
the  intending  purchaser. 
This  will  leave  the  owner  with  only  non-reacting  and  presum- 
ably healthy  animals.  But  even  if  the  herd  is  a self-supporting 
one,  mainly  or  entirely  recruited  by  animals  bred  on  the  place, 
it  must  afterwards  be  tested  every  six  months.  This  may  appear 
an  onerous  undertaking,  but  those  who  are  not  prepared  to 
carry  it  out  w.ould  be  well  advised  not  to  incur  the  trouble  and 
expense  connected  with  the  initial  measures  of  eradication. 
Every  new  animal  introduced  into  the  herd,  whatever  its 
age,  sex,  or  value,  must  be  quarantined  for  one  month  after 
purchase  and  then  tested.  If  it  does  not  react  it  may  be 
allowed  to  mix  with  the  other  animals,  but  it  should  be 
re-tested  within  two  or  three  months.  These  precautions  are 
