Tuberculosis. 
31 
calves  are  infected  with  tubercle  bacilli  within  a few  days 
or  weeks  of  their  birth,  visible  disease  develops  in  them  with 
even  greater  rapidity  than  in  older  animals.  In  reality  such 
experiments  are  not  needed,  in  view  of  the  admitted  fact  that 
extensive  tuberculous  lesions  have  in  hundreds  of  cases  been 
found  in  newly-born  calves,  although  the  proportion  of  calves 
showing  visible  lesions  at  birth  is  small. 
Finally,  the  theory  now  being  discussed  has  been  absolutely 
disproved  by  the  evidence  accumulated  in  recent  years  to  show* 
that  when  calves  born  of  tuberculous  cows  are  promptly 
removed  from  their  dams  and  kept  under  conditions  that 
prevent  infection  after  birth,  they  do  not  become  tuberculous. 
It  may  therefore  be  accepted  as  a well-grounded  estimate 
that  among  the  calves  born  of  actually  tuberculous  cows,  on  an 
average  not  more  than  one  in  fifty,  and  possibly  not  one  in  a 
hundred,  inherits  the  actual  disease.  As  will  afterwards  be 
pointed  out,  account  must  be  taken  of  the  possibility  that  a 
new-born  calf  may  be  tuberculous,  when  one  is  devising 
measures  for  the  eradication  of  the  disease  from  a herd,  but  it 
cannot  be  admitted  that  congenital  tuberculosis  is  to  any 
appreciable  extent  responsible  for  the  present  prevalence  of 
the  disease  among  cattle. 
It  has  already  been  pointed  out  that  the  view  that  the  actual 
disease  is  often  transmitted  from  the  parent  to  the  unborn 
progeny  was  first  put  forward  to  explain  the  fact  that  in  the 
human  species  tuberculosis  often  runs  in  families,  and  that  the 
same  view  was  with  less  justification  extended  to  bovine 
tuberculosis  also.  The  belief  that  this  method  of  transmission 
plays  an  important  role  in  human  tuberculosis  is  no  longer 
held  by  medical  pathologists,  and  the  discredit  under  which  it 
has  fallen  is  in  great  measure  due  to  the  evidence  cited  above 
to  prove  the  comparative  rarity  of  congenital  tuberculosis 
among  cattle.  But  direct  evidence  of  quite  the  same  kind 
exists  to  prove  that  only  an  insignificant  proportion  of  the 
children  of  tuberculous  parents  are  born  with  the  disease  in 
them.  The  countless  opportunities  afforded  by  post-mortem 
examination  of  young  children  have  not  yet  led  to  the 
detection  of  fifty  cases  of  congenital  tuberculosis  in  the  human 
species. 
There  is  not  the  least  mystery  regarding  the  manner  in 
which  the  disease  is  contracted  during  intra-uterine  life.  The 
cases  in  which  calves  are  infected  prior  to  birth  are  cases  in 
which  the  womb  of  the  cow  is  itself  the  seat  of  tuberculous 
disease.  When  that  organ  is  diseased  there  is  a likelihood  that 
some  of-  the  tubercle  bacilli  in  its  wall  will  find  their  way 
into  the  body  of  the  foetus,  but  as  long  as  the  womb  remains 
healthy  the  foetus  is  in  little  or  no  danger  of  infection,  no 
