Am.  Jour.  Pharm. 
April,  19 19. 
Studies  on  Pepsin. 
235 
purified  material  was  dried  to  a  constant  moisture  content  of  about 
5  per  cent,  and  scaled.  Assays  for  proteolytic  power  were  then 
carried  through  and  the  samples  analyzed  chemically. 
Determination  of  the  proteolytic  strength  of  the  different 
samples,  made  in  association  with  our  colleagues,  L.  M.  Gerdes  and 
W.  L.  Seibert,  was  in  accordance  with  the  method  given  in  the 
ninth  revision  of  the  U.  S.  Pharmacopoeia.8  The  assays  were 
checked  in  each  case,  and  controlled  by  running  through  a  standard 
(1:3,000)  pepsin  under  identical  conditions. 
The  chemical  examination  included  analyses  of  total  mineral  mat- 
ter, total  nitrogen,  total  sulphur  by  the  method  of  Wolf  and  Oster- 
berg9  volumetric  estimation,  in  the  ash,  of  phosphoric  acid  as  P205,10 
chlorides  as  NaCl,11  calcium  as  CaO ;  also,  determination  of  nitrogen 
existing  in  coagulable  protein,  proteoses  by  zinc  sulphate  precipita- 
tion,12 peptones  by  Bigelow  and  Cook's13,  modification  of  Sjerning's 
method,  and  amino  acids  according  to  Van  Slyke.14  In  addition, 
observations  were  made  in  a  2  per  cent,  aqueous  solution  of  optical 
rotation,  and  of  the  hydrogen-ion  concentration.  The  direct  read- 
ing ionometer  described  by  Bartell15  was  used  in  the  latter,  with  a 
Weston  Standard  Cell,  and  the  chain :  Calomel  electrode  (N  KC1)  — 
saturated  KC1 — pepsin  solution — Pt.  electrode — H2  at  23  °.  The 
complete  "  set  up  "  employed  wras  similar  to  that  used  by  Davis16  in 
a  previous  investigation  of  diphtheria  toxin. 
Supplementing  the  preceding,  qualitative  tests  were  carried  out 
in  accordance  with  the  technique  employed  by  one  of  us,  Davis,17 
with  peptone  samples.  Both  a  straight  2  per  cent,  aqueous  solution 
and  the  filtrate,  after  coagulating  the  protein,  were  used,  and  ex- 
amination made  for :  tyrosin   (xanthoproteic,  Millon's  reaction) 
8  "  Pharmacopoeia  of  the  United  States,"  1916,  p.  312,  9th  rev.,  P.  Blakis- 
ton's  Son  &  Co. 
9  Wolf  and  Osterberg,  Biochem.  Z.,  vol.  29,  429,  1910. 
10  "Methods  of  Analysis,  A.  O.  A.  C,"  U.  S.  Dept.  Agr.,  Bur.  Chem., 
Rev.  Bull,  107,  4,  1912. 
11  "  Standard  Methods  of  Water  Analysis,"  ^77?.  Pub.  Health  Ass'n,  1917, 
p.  4. 
12  Bomer,  Z.  anal.  Chem.,  vol.  5,  562,  1895. 
13  Bigelow  and  Cook,  Journal  of  the  American  Chemical  Society,  vol.  38, 
1496,  1906. 
14  Van  Slyke,  /.  Biol.  Chem.,  vol.  16,  121,  1913. 
15  Bartell,  Journal  of  the  American  Chemical  Society,  vol.  39,  630,  1917. 
16  Davis,  /.  Lab.  Clin.  Med.,  vol.  3-  358,  1918. 
17  Davis,  ibid.,  vol.  3,  75,  1917- 
