AmFe°bU'i8P86arm" }  The  Albuminoids  of  Milk.  95 
THE  ALBUMINOIDS  OF  MILK. 
By  A.  Dogiel. 
1.  Peptones. — As  a  result  of  his  investigation  of  cow's  milk, 
Schmidt-Mulheim  states  that  it  contains  peptones,  the  proportion 
varying  from  0*08  to  0*19  per  cent,  of  the  milk  (Pfluger's  Archiv, 
28,  287).  Hofmeister,  on  the  other  hand,  denies  that  they  are  present, 
and  in  human  milk  likewise  (Zeits.  physiol.  Chem.,  2,  288).  In  further 
investigating  this  question,  the  author  sought  first  to  ascertain  the 
probable  error  inherent  in  the  method  of  isolating  the  peptones.  For 
this  purpose  known  quantities  of  peptones  were  added,  and  the  milk 
was  then  treated  with  ferric  chloride  solution  in  the  usual  way  for  the 
separation  of  other  protei'ds ;  the  peptones  were  estimated  in  the  filtrate 
by  means  of  a  comparative  colorimetric  determination  based  on  the 
biuret  reaction.  In  19  experiments  in  which  40  c.c.  of  milk  were 
taken  for  each,  the  quantities  of  peptones  added  varied  from  O0Q4  to 
O020  gram,  and  the  solutions  finally  obtained,  after  precipitation  and 
washing,  amounted  to  190 — 250  c.c.  The  ultimate  result  was  to 
show  that  the  quantity  of  peptone  retained  by  the  precipitate  was 
independent  of  the  amount  added,  the  quantity  lost  being  approxi- 
mately 0*005  in  each  experiment,  that  is,  0'0023  for  every  100  c.c. 
solution  ultimately  obtained.  That  the  peptone  is  retained  by  the 
precipitate  is  proved,  according  to  the  author,  by  the  diminished  loss 
which  is  noted  when  the  iron  oxide  precipitate  is  boiled  with  water, 
and  this  aqueous  extract  added  to  the  solution.  By  varying  the 
quantity  of  milk,  it  was  found  that  the  loss  of  peptone  remained 
equally  uninfluenced. 
On  the  basis  of  the  experience  of  these  blank  experiments,  the 
author  proceeded  to  the  examination  of  normal  specimens  of  cow's 
and  woman's  milk,  adopting  special  precautions  in  the  isolation  by 
precipitation  of  the  peptones  presumed  to  be  present.  In  all  cases, 
however,  negative  results  were  obtained.  Having  further  repeated 
Schmidt-Mulheini's  experiments  (loc.  cit.),  and  found  that  the  sub- 
stance supposed  by  him  to  be  a  peptone  is  a  residue  merely  of  one  of 
the  normal  proteids  of  milk,  the  author  finally  concludes  that  these 
milks  do  not  contain  peptones. 
2.  Caseins. — The  author  has  isolated,  with  special  precautions,  the 
caseins  from  woman's  and  from  cow's  milk  for  the  purpose  of  institut- 
ing a  comparison  of  their  properties.    Having  found  that  their  reac- 
