Am-s^-1f8h9arm-}  Acid  Fermentation  of  Milk  481 
The  casein  evidently  plays  a  part — an  important  part,  but  what 
part  ?  Liebig  maintained  that  casein  was  itself  the  ferment,  but  Pas- 
teur proved  the  germs  indispensable.  Pasteur's  mistake  lay  in  con- 
sidering the  casein  only  a  food  for  the  germs. 
What  is  our  author's  opinion  ?  He  holds,  as  he  explained  two 
years  ago,  that  animal  protoplasm,  as  blood,  muscle,  etc.,  has  the  power, 
without  the  aid  of  germs,  of  turning  starch  into  sugar  and  sugar  into 
acid ;  casein  resembles  animal  protoplasm  in  this  respect,  and  conse- 
quently in  the  souring  of  milk  two  factors  are  at  work,  one  acid  fer- 
mentation being  due  to  the  casein  and  another  to  the  germs.  If  this 
be  true,  the  place  of  the  casein  might  be  taken  by  other  substances. 
He  finds  that  it  is  so.  Coagulated  albumen  and  yoke  of  egg  have  a 
particularly  powerful  action.  He  found  also  that  heating  the  casein 
for  one  and  one-quarter  hours  (in  steam  of  five  atmospheres  pressure) 
had  no  effect  in  diminishing,  but  even  increased  its  power  as  a  fer- 
ment. *  Is  the  action  then  purely  mechanical,  depending  like  that 
of  platinum  sponge  on  porosity  ?  It  seems  not.  Wadding  and 
amber  have  no  effect ;  glass-wool,  by  giving  alkali  to  the  fluid,  even 
diminishes  its  acidity.  Sponge  slightly  increases  it,  owing  to  its  animal 
basis. 
One  may  conclude  then  that  this  "power  of  furthering  the  produc- 
tion of  acid  "  is  peculiar  to  animal  substances.  The  method  of  action 
we  do  not  know  and  vital  (Wirkungen  der  Lebenserscheinungen)  is  the 
adjective  Fokker  would  apply  to  it,  life,  however,  being  always  considered 
resolvable  into  simple  chemical  action.  What  part  do  the  bacteria  take  ? 
Fermentation,  we  know,  is  impossible  without  them.  The  germ,  as 
he  poetically  puts  it,  is  the  spark  that  kindles  the  firework — 
that  it  turns  out  a  pillar  or  a  temple,  depends  not  on  the  spark, 
but  on  the  construction  of  the  firework;  and,  as  a  spark  from 
another  fire  or  a  spark  from  a  match  box  begins  it  equally  well, 
.  so  also,  according  to  Grotenfeld,  the  fermentation  may  be  set  agoing 
by  the  regulation  germ,  ofr  by  an  ordinary  saprophyte  a  little  bit 
modified. 
Our  author  is  by  and  bye  to  give  us  the  result  of  further  researches 
on  the  subject.  He  has  found  in  the  atmosphere  about  a  goat  and  on 
the  hairs  of  the  same  animal  bacteria  capable  of  souring  sterilized 
milk.  He  found  numerous  others,  but  none  capable  of  curding  and 
acidifying  to  the  same  extent  or  with  the  same  rapidity  as  the  germ 
in  ordinary  sour  milk. 
