42 
Casein  in  Milk. 
Anj.  Jour.  Pharm 
Jarj.,188«i. 
CASEIN  IN  MILK,  AND  ON  THE  ACTION  OF  RENNET. 
By  W.  Eugling. 
The  addition  of  ammonium  oxalate  to  milk  does  not  precipitate 
the  calcium  salt?,  but  if,  after  the  addition  of  the  oxalate,  calcium 
chloride  be  added,  then  casein  is  separated  and  carries  calcium  oxa- 
late down  with  it;  it  is  considered  that  calcium  is  in  a  definite  organic 
combination  with  casein,  and  this  combination  must  first  be  destroyed 
before  calcium  can  be  separated  as  oxalate.  The  calcium  albumi- 
nates in  milk  resemble  basic  salts,  and  are  readily  decomposed  by 
acetic,  lactic,  and  tartaric  acids,  but  not  by  benzoic  acid,  etc.  When 
acetic  acid  has  been  added  and  then  ammonium  oxalate,  calcium 
oxalate  may  be  recognized  by  the  microscope,  although  the  quantity 
of  acid  has  been  insufficient  to  coagulate  the  milk.  Mineral  acids, 
except  boric  and  arsenious  aoids,  act  like  strong  organic  acids ; 
at  the  same  time  as  calcium  is  in  combination  with  casein  as  a 
basic  salt,  phosphates  are  carried  down  with  the  coagulum.  Schreiner 
has  stated  that  when  milk  is  boiled,  sulphuretted  hydrogen  is 
evolved,  but  Eu^lin^  is  unable  t:>  corroborate  that  statement,  as 
he  has  found  the  percentage  of  sulphur  belore  and  after  boiling 
to  be  the  same,  although  various  samples  of  milk  differ  in  their 
percentage  of  sulphur;  the  change  which  the  author  believes  to 
occur  on  boiling  is  that  a  part  of  the  phosphates  dissolved  by  the 
alkaline  phosphates  of  the  serum  pass  by  the  action  of  heat  out 
of  the  serum  and  combine  with  the  casein  compounds,  the  result 
being  the  formation  of  an  alkaline  albuminate;  consequently  the 
milk  has  an  alkaline  reaction.  This  statement  is  supported  by  the 
results  of  the  analysis  of  milk  (fresh  and  boiled)  after  addition  of  alco-^ 
hoi,  which  separates  casein,  combined  with  a  larger  quantity  of  calcium 
if  the  milk  has  been  boiled  than  when  it  is  fresh.  It  is  because  of  this 
rearrangement  of  the  constituents  of  milk  after  boiling,  that  it 
becomes  alkaline,  and  that  rennet  has  no  action  on  boiled  milk;  but  if 
an  acid  be  added  so  as  to  bring  back  the  original  condition  by  destroy- 
ing the  alkaline  albuminate,  the  rennet  produces  its  well-known 
effects.  It  is  possible  that  the  action  of  rennet  is  to  hydrolise  a  part 
of  the  milk  albuminates,  whereby  its  combinations  with  calcium 
phosphates  are  rendered  less  stable ;  in  proof  of  this,  it  is  stated  that 
although  calcium  is  not  recognisable  by  means  of  ammonium  oxalate 
in  the  serum  produced  by  the  addition  of  alcohol  or  sodium  chloride, 
