Am.  Jour.  Pharm. 
Nov.,  1884. 
Milk. 
591 
MILK. 
By  E.  Duclaux. 
The  albuminoid  matter  in  milk  may  be  divided  into  colloidal  casein, 
casein  in  suspension,  and  soluble  casein,  the  latter  •  being  capable  of 
passing  through  biscuit  earthenware.  Small  battery  cells  give  good 
results,  but  the  larger  cells  do  not  yield  a  filtrate  of  constant  composi- 
tion, even  from  the  same  milk,  in  consequence  of  inequalities  in  the 
earthenware.  This  method  of  filtration  separates  those  substances  which 
are  in  suspension,  i.  e.,  fat,  casein,  etc.,  from  those  which  are  in  solution, 
k  e.,  sugar,  inorganic  salts,  etc.  The  original  milk  and  the  filtrates 
were  examined  by  the  methods  described  in  the  author's  memoir 
(Ann.  de  VInstitut  Agronomique,  1879-1880).  The  following  results 
were  obtained  with  a  sample  of  Cantal  milk  : 
In  suspension.  In  solution. 
Fat   3-32   
Sugar   4-98 
Casein                                         3*31  0*84 
Calcium  phosphate                        0*22  014 
Inorganic  salts   0*39 
6-75  6-35 
In  this  case,  the  soluble  casein  is  about  one-fifth  of  the  total  casein, 
but  the  proportion  is  rarely  so  high  ;  in  Cantal  milk,  the  amount  of 
soluble  casein  varies  between  4  and  6  grams  per  litre;  this  proportion 
remains  approximately  constant,  and  does  not  sensibly  change,  even 
when  the  milk  is  kept  for  a  considerable  time.  It  is  only  slighlly 
affected  by  the  action  of  heat ;  the  filtrate  becomes  turbid  on  boiling, 
but  the  precipitate  is  very  slight,  and  gradually  redissolves.  The 
action  of  heat  on  the  other  two  varieties  of  casein  causes  them  to 
agglomerate,  and  the  deposit  inside  the  porous  cell  after  filtration  is 
always  more  compact  if  the  milk  has  been  boiled.  Slight  acidity 
causes  a  portion  of  the  colloidal  casein  to  pass  into  the  suspended 
condition,  and  slight  alkalinity  converts  some  of  the  suspended  casein 
into  the  colloidal  form,  but  neither  of  these  conditions  has  any  effect 
on  the  soluble  casein.  The  proportion  of  soluble  casein  in  normal 
milk  is  not  only  approximately  constant,  but  seems  to  be  independent 
of  the  nature  of  the  milk,  and  is  sensibly  the  same  in  the  milk  of  cows 
from  various  districts,  in  goats',  asses',  and  human  milk.  The  porpor- 
tion  of  soluble  casein  is  increased  to  a  slight  extent  by  the  addition 
