AmApXi9i™'  '  Studies  on  Pepsin.  233 
reader  to  evaluate  the  barks  commercially,  as  well  as  to  derive  useful 
additional  scientific  information  from  them. 
[Contribution  from  the  Research  Laboratory  and  the  Department  of  Glandu- 
lar Extracts,  Parke,  Davis  &  Co.] 
STUDIES  ON  PEPSIN.    I.  CHEMICAL  CHANGES  IN 
THE  PURIFICATION  OF  PEPSIN.1 
By  Lewis  Davis  and  Harvey  M.  Merker. 
The  question  of  the  chemical  composition  of  pepsin  has  occupied 
the  attention  of  a  number  of  investigators.  Following  the  classical 
researches  of  Pawlow2  and  his  pupils,  Pekelharing3  appears  to 
have  been  the  first  to  undertake  purification  of  the  enzyme.  This 
investigator  prepared  a  light  yellow  powder  which,  while  readily 
soluble  in  dilute  acids  and  sodium  chloride  solution,  dissolved  with 
difficulty  in  water  but  showed  strong  peptic  activity.  It  gave  reac- 
tions for  albumin,  but  was  believed  to  contain  a  soluble  phosphorus 
compound  as  an  impurity.  On  boiling  pepsin  solutions,  Pekelharing 
obtained  a  nucleoproteid  and  was  able,  under  certain  conditions,  to 
separate  an  albumose. 
Nencki  and  Sieber,4  using  as  initial  material  juice  obtained 
through  gastric  fistula  in  dogs,  claim  to  have  secured  an  active 
pepsin  preparation  through  precipitation  which  is  free  from  albumin. 
At  the  same  time,  they  consider  the  precipitate  of  transparent 
granules  containing  chlorine  which  they  obtained  by  strongly  cooling 
the  gastric  juice  to  be  a  chemical  individual,  and,  in  all  probability, 
the  true  enzyme.  They  also  submit  analyses  to  support  their  con- 
tentions. Pekelharing,5  in  a  later  investigation,  in  which  he  em- 
ployed the  artificial  gastric  juices  extracted  from  several  hundred 
hog  stomachs  by  his  previous  method,  and  also  the  juice  obtained 
from  gastric  fistula  in  dogs,  disproved  this  view.    He  found  pepsin 
1  Read  before  the  Biological  Section  of  the  American  Chemical  Society 
at  the  Cleveland  meeting,  September  12,  1918.  Reprinted  from  The  Journal 
of  the  American  Chemical  Society,  February,  1919. 
2  Pawlow,  Centr.  Physiol,  1888;  Ergcbnissc  Physiol.,  1902,  i.  Part  I.  246. 
3  Pekelharing,  Z.  physiol.  Chcm.,  vol.  22,  233.  1897. 
4  Nencki  and  Sieber,  ibid.,  vol.  23,  291,  1901. 
5  Pekelharing,  ibid.,  vol.  35,  8,  1902. 
