AmApJrTi^rm1       Germicidal  Properties  of  Milk.  281 
THE  ALLEGED  GERMICIDAL  PROPERTIES  OF  MILK.* 
More  than  thirty  years  have  elapsed  since  Nuttall,  investigating 
the  mechanism  of  natural  immunity,  demonstrated  experimentally 
that  blood  possesses  the  power  of  killing  bacteria.  Soon  afterward 
the  investigation  of  such  bactericidal  power  was  extended  to  other 
body  fluids.  A  somewhat  comparable  phenomenon  has  been  ob- 
served in  the  case  of  milk,  but  the  explanation  of  what  takes  place 
has  been  the  subject  of  active  debate.  The  facts  are  these :  When 
freshly  drawn  milk  stands  without  being  manipulated  in  any  way, 
an  apparent  decrease  in  the  number  of  bacteria  that  it  contains 
takes  place  within  a  short  time.  This  behavior  is  seen  only  in  raw 
milk,  never  being  observed  in  milk  that  has  been  heated  to  any 
considerable  extent.  With  respect  to  the  temperature  at  which 
the  milk  is  deprived  of  this  potency,  opinions  have  varied.  A  num- 
ber of  bacteriologists  have  stated  that  the  rapid  decrease  in  the 
number  of  micro-organisms  in  raw  milk  is  apparent  rather  than 
real.  They  ascribe  the  results  actually  observed  to  an  agglutination 
of  the  bacteria  present  so  that  a  smaller  number  of  colonies  may 
exhibit  themselves  in  the  modes  of  counting  currently  employed, 
although  no  fewer  organisms  are  actually  encountered.  Should 
this  be  true,  it  would  obviously  be  a  misnomer  to  speak  of  the 
germicidal  properties  of  milk.  Chambers1  has  recently  subjected 
the  problem  to  a  renewed  investigation  at  the  University  of  Illinois. 
The  combined  evidence  of  microscopic  examination  and  plate  count 
demonstrates  a  bactericidal  property,  or  actual  decrease  in  number 
of  bacteria  in  raw  milk  under  certain  conditions.  Part  of  the 
earlier  discrepancies  lay  in  the  failure  to  recognize  that  the  germi- 
cidal action  is  specific,  depending  on  the  individual  animal  and  on 
the  species  of  bacteria  involved.  In  the  freshly  drawn  mixed  milk 
from  a  herd  of  cows,  the  bacterial  inhibition  may  therefore  be 
variable.  When  only  the  total  number  of  micro-organisms  in  the 
milk  is  considered,  a  decrease  in  numbers  may  be  evident,  or  one 
unaffected  strain  by  its  rapid  increase  may  completely  hide'  the 
germicidal  action  on  another  less  numerous  strain.  Chambers  sug- 
gests that  the  predominance  of  lactic  acid  forming  organisms  with 
the  increasing  age  of  the  milk  might  be  attributed  to  bacterial 
inhibition;  for  these  organisms  are  apparently  unaffected  by  it, 
*From  Jour.  Amer.  Med.  Assoc.,  March  12,  1921. 
1  Chambers,  W.  H. :  Bacterial  Inhibition,  I,  Germicidal  Action  in  Milk, 
J.  Bacteriol.  5 :  527  (Nov.)  1920. 
