Am.  Jour.  Pliarm. ) 
Feb.,  1881.  / 
Peptone. 
79 
mercial  or  prepared  by  extracting  pig's  or  dog's  gastric  mucous  mem- 
brane in  glycerol)  for  2  to  5  hours  at  40 °C.  The  solution  was  then 
neutralized  until  the  reaction  was  very  feebly  acid^  heated  to  boiling, 
and  filtered  hot.  The  filtrate  after  cooling,  usually  opaslescent  or  dis- 
tinctly cloudy,  was  evaporated  a  little,  made  strongly  acid  with  acetic 
acid,  and  saturated  with  sodium  chloride.  The  somewhat  abundant 
fiocculent  precipitate  so  produced  was  filtered  off,  after  8  to  12  hours. 
The  fluid,  which  filters  readily,  passes  perfectly  clear  through  the 
paper,  and  the  precipitate  dissolves  very  readily  in  distilled  water  on 
warming,  still  not  without  a  slight  flocculent  cloudiness,  due  to  albu- 
min which  has  not  been  completely  precipitated  by  boiling  in  a  feebly 
acid  solution,  but  when  precipitated  by  sodium  chloride  and  acetic  acid, 
is  not  soluble  on  heating.  If  the  precipitate  is  dissolved  in  a  suffi- 
ciency of  water,  the  fluid,  when  separated  from  the  albuminoid  preci- 
pitate, is  perfectly  clear ;  if,  however,  the  distilled  water  be  spared, 
with  the  idea  of  avoiding  a  large  mass  of  fluid,  the  precipitate  will 
return  on  cooling.  The  solution  is  then  to  be  dialyzed,  in  order  to  get 
rid  of  the  acetic  acid  and  sodium  chloride;  in  one  day,  a  precipitate  of 
peptone  is  formed,  which  continually  increases  as  the  dialysis  is  pushed, 
and  which  on  warming,  or  the  addition  of  small  quantities  of  acid, 
alkali  or  salts,  is  completely  dissolved.  After  three  or  four  days' 
dialysis,  the  fluid  is  nearly  free  from  salts,  and  the  precipitate  may  be 
removed  from  the  dialyser,  boiled  in  water,  and  the  resulting  solution, 
which  is  not  quite  clear,  filtered  hot.  The  filtrate  is  a  pure  peptone 
solution,  and  will  yield  a  heavy  precipitate  on  cooling.  It  is  to  be 
concentrated  at  a  gentle  heat,  and  finally  dried  in  a  vacuum  over  sul- 
phuric acid.  When  dry,  peptone  so  prepared  is  a  pure  white  powder, 
and  is  not  hygroscopic.    It  has  the  following  properties  : 
Heated  over  a  flame,  it  does  not  melt,  but  forms  strong  tenacious 
bubbles.  The  ash  is  small ;  the  substance  heated  at  105°  gave  0*4 
per  cent,  and  0*47  per  cent.  ash. 
The  powder  is  only  partially  soluble  in  cold  water,  but  dissolves 
completely  on  warming,  separating  again  as  the  solution  cools.  The 
solution  has  a  perfectly  neutral  reaction. 
Addition  of  a  small  quantity  of  sodium  chloride  will  prevent  pre- 
cipitation on  cooling ;  added  in  excess,  however,  it  causes  a  slight 
turbidity  in  the  cold,  which  disappears  on  warming. 
Very  small  quantities  of  acids  or  alkalies  will  cause  solution  in  the 
cold.  Peptone  is  precipitated  from  the  alkaline  solution  by  sodium 
chloride  in  excess ;  this  does  not  occur,  however,  if  the  peptone  is 
