28 
Tuberculosis. 
organism  into  the  previously  healthy  body.  Koch’s  researches 
regarding  the  characters  of  the  tubercle  bacillus  may  also  be 
said  to  have  made  highly  probable  what  has  now  come  to  be 
accepted  as  a settled  fact,  viz.,  that  the  tubercle  bacillus  in 
natural  circumstances  never  multiplies  except  in  the  bodies  of 
tuberculous  subjects  ; and  from  this  follows  the  all-important 
conclusion  that  tuberculosis  cannot  have  any  other  origin  than 
the  introduction  into  the  healthy  subject  of  tubercle  bacilli 
derived  from  an  antecedent  case  of  the  same  disease. 
As  the  special  purpose  of  this  article  is  to  examine  the 
evidence  bearing  on  the  influence  of  heredity  in  the  dissemina- 
tion of  tuberculosis  in  cattle,  it  is  necessary  to  note  here  that 
the  belief  in  the  importance  of  that  influence  which  became 
common  among  breeders  and  veterinary  surgeons  never  had 
the  same  justification  as  the  like  view  regarding  the  part 
played  by  heredity  in  human  tuberculosis.  In  settled  or 
civilised  communities  of  human  beings  the  tendency  of 
tuberculosis  to  run  in  families  is  always  obvious,  and  every  one 
can  quote  numerous  examples  of  it  which  have  come  under 
his  own  observation,  but  there  never  has  been  evidence  of 
like  extent  to  show  that  tuberculosis  is  strikingly  frequent 
among  the  progeny  of  tuberculous  cows  or  bulls.  The  fact 
appears  to  be  that  the  belief  in  the  importance  of  heredity  in 
the  spread  of  the  bovine  disease  was  in  large  measure  borrowed 
from  human  pathology,  and  was  not  a view  naturally  suggested 
by  the  observed  facts  in  connection  with  animal  tuberculosis. 
, 
Inheritance  of  the  Disease  itself,  or  Congenital 
Tuberculosis. 
After  the  discovery  of  the  tubercle  bacillus  by  Koch, 
the  view  that  inheritance  of  a special  predisposition 
to  the  disease  was  of  prime  importance  for  a time  declined 
in  favour  of  the  belief  that  the  actual  disease  was  often 
inherited  from  a diseased  parent.  Although,  as  previously 
stated,  it  was  the  facts  observed  in  connection  with  the  human 
disease  that  suggested  the  importance  of  heredity  in  the 
causation  of  tuberculosis,  the  belief  that  the  actual  disease  was 
frequently  inherited  was  first  disproved,  or  at  least  made 
highly  improbable,  by  observations  made  regarding  the  bovine 
disease. 
These  observations  were  made  in  certain  of  the  large 
Continental  abattoirs,  and  they  showed  that  the  number  of 
cases  of  tuberculosis  encountered  among  the  calves  slaughtered 
within  a month  of  their  birth  was  remarkably  low  when 
compared  with  the  number  of  cases  encountered  among  the 
cows  killed  at  the  same  place.  Some  of  the  earlier  statistics 
collected  in  this  way  appeared  to  show  that  not  more  than  one 
