58  New  Method  for  Preparing  Pepsin. 
Am.  Jour.  Pharkv 
Feb.  1, 1872. 
properties,  I  examined  this  and  found  that,  although  slower  in  its- 
action,  it  still  dissolved  albumen,  and  was  also  precipitated  by  chloride- 
of  sodium. 
It  seems,  therefore,  that  the  glycerin  in  the  preparation  of  liquid 
pepsin  prevented  the  pepsin  from  decomposition. 
In  the  spring  I  had  set  aside  moist  precipitate  (by  chloride  of  sodium) 
of  pepsin  of  the  consistence  ready  for  the  press  ;  when  examined  after 
six  months  it  had  a  sweet  odor,  was  pressed,  dried,  and  its  digestive 
power  ascertained,  whereby  it  proved  to  have  the  same  digestive 
strength  as  when  fresh  prepared. 
Several  times  the  (chloride  of  sodium)  precipitate,  while  draining 
on  the  cloth,  was  entirely  frozen  through,  but  proved,  after  thawing 
not  inferior  in  quality. 
The  purified  as  well  as  the  saccharated  pepsin,  examined  twelve 
months  after  preparation,  proved  to  be  entirely  as  good  as  when  re- 
cently prepared  ;  they  had  lost  nothing  of  their  strength,  and  dis- 
solved albumen  in  the  same  time  and  in  the  same  quantities  as  when 
quite  fresh.  The  only  difference  is,  that  with  age  the  dry  pepsin 
dissolves  somewhat  slower  in  acidulated  water. 
Action  of  Pepsin  on  Milk. — As  the  opinion  is  still  prevalent, 
even  amongst  physicians,  that  only  calf  rennet  has  the  property  of 
separating  the  casein  from  the  milk,  or,  in  other  words,  to  coagulate 
milk,  it  was  interesting  to  me  to  try  the  action  of  pepsin  on  milk. 
Five  grains  of  saccharated  pepsin,  swelled  in  a  little  water  and  then- 
stirred  into  one  pint  of  milk,  coagulated  the  milk  in  30  minutes. 
Of  a  solution  of  two  grains  of  purified  pepsin,  two  drops  of  hydro- 
chloric acid  and  one  fluid-ounce  of  water,  it  took  five  drops  to  coagu- 
late four  ounces  of  milk  in  about  20  to  30  minutes ;  while  10  drops 
of  dilute  muriatic  acid  (20  drops  to  one  oz.  of  water)  did  not  curdle 
four  oz.  of  milk  in  four  hours. 
Averaging  400  drops  in  a  fluid-ounce  of  the  pepsin  solution,  it 
took  one-fortieth  (J^)  part  of  one  grain  to  coagulate  four  ounces  of 
milk  or  one  grain  to  five  quarts  ;  according  to  this  test,  one  part  of 
pepsin  will  coagulate  about  80,000  (eighty  thousand)  parts  of  milk. 
The  success  of  these  experiments  depends  a  great  deal  on  the  tem- 
perature ;  the  best  way  is  to  add  the  pepsin  to  the  milk  when  cold, 
and  then  heat  it  slowly ;  when  kept  cold  it  takes  much  longer  time 
to  coagulate  the  milk.    Also  when  the  milk  is  heated  first,  say  to- 
