Am.  Jour.  Pliariri.) 
.lull.,  188-2.  j 
Activity  of  P(incr€((tic  Extracts. 
2r 
extracts.  Tlic  reaction  in  question  depends  on  the  production,  as  a 
first  step  in  the  digestion  of  casein,  of  a  modified  form  of  that  body  — 
termed  by  the  author  "  metacasei'n'^ — which  resembles  casein  in  being 
curdled  by  acetic  acid  in  the  cold,  but  differs  from  it  in  being  curdled 
also  by  simple  boiling.  These  two  reactions  together  distinguish  meta- 
casein  from  all  other  proteids.  The  property  of  curdling  wdien  boiled, 
which  may  be  called  the  metacctsein  reaction,  continues  observable  in. 
milk  undergoing  tryptic  digestion  until  near  the  end  of  the  process;: 
it  then  disa])penrs  somewhat  abruptly,  the  milk  remaining  tluid  when, 
boiled.  We  may  therefore  speak  of  the  onset-point  and  the  vanishing- 
point  of  the  inetacasei'n  reaction,  these  two  points  marking  respect- 
ively the  initial  and  terminal  limits  of  the  principal  pha,ses  in  the- 
digestion  of  milk  by  pancreatic  extract.  Before,  howev^er,  the  onset- 
point  of  the  reaction,  i.  e.,  distinct  curdling,  is  attained,  its  approachi 
is  indicated  by  an  appearance  of  soiling  of  the  sides  of  the  test-tube  in 
which  the  milk  has  been  boiled.  This  appearance  is  due  to  incipient 
coagulation,  which  presently  develops  into  pronounced  curdling. 
When  milk  is  diluted  with  water,  the  occurrence  of  the  metacasein' 
reaction  is  postponed,  the  time  of  ])ostponement  varying  with  the 
degree  of  dilution. 
The  method  of  trypsimetry  ado})ted  by  the  author  consists  in  ascer- 
taining how  many  cubic  centimeters  of  milk  can  be  brought  to  the 
onset  of  the  metacasein  reaction  in  five  minutes  by  1  cc.  of  the  extract 
to  be  tested  at  a  given  temperature,  attention  being  paid,  as  in  the 
case  of  disastase,  to  the  relations  of  tryptic  action  to  (quantity,  time 
and  temperature. 
The  rule  of  inverse  relation  between  quantity  and  time,  which  was 
found  to  be  valid  within  a  wide  range  in  the  case  of  disastase  and 
starch,  holds  good  in  the  case  of  tryspin  and  milk  within  narrow 
limits  only.  When  the  time  of  action  exceeds  eight  or  ten  minutes 
the  advent  of  the  metacasein  reaction  is  postponed  beyond  the  term 
indicated  by  the  rule  of  inverse  proportion,  and  this  postponement 
increases  as  the  time  of  action  is  lengthened.  When  the  vanishing- 
point  of  the  metacaseVn  reaction  is  taken  as  the  point  of  comparison, 
the  results  aj)|)roximate  more  nearly  to  the  rule  of  inverse  proportion, 
('spe(;ially  at  low  tem])eratures ;  nevertheless  the  evidence  points  in  the 
same  dirciction,  indicating  that  trys])iii,  like  diastase,  exhausts  itself  in 
action  at  a  ])r<)gressively  retarded  rate.  When  the  onset-point  of  the 
reaction  falls  between  three  and  six  minutes,  the  inverse  time-rate 
gives  a  trustworthy  basis  of  cahudation,  but  not  beyond  these  limits. 
