Am.  Jour.  Pharm. 
Nov.,  19  iS. 
Diphtheria  Antitoxin. 
773 
from  proteins  by  digesting  these  away  by  means  of  trypsin,76  but 
this  work  could  not  be  confirmed  by  Mellanby,  Banzhaf,77  Pick,  or 
Brieger.7S 
Other  work  would  indicate  that  the  antitoxic  power  of  the  serum 
is  in  relation  to  the  percentage  of  the  proteins,  hence  a  protein. 
According  to  Mellanby,  heating  and  freezing  both  show  that  the 
concentration  of  the  antitoxin  follows  the  concentration  of  the  pro- 
tein on  approximately  parallel  lines. 
As  Schryver  says :  "  Not  sufficient  is  know  yet  of  the  true  chem- 
ical structure  of  the  proteins  to  found  a  rational  classification  based 
upon  differences  of  chemical  constitution.  The  classification 
adopted  therefore  is  more  or  less  of  an  empirical  nature,  founded 
only  to  a  small  extent  on  chemical  distinctions,  but  chiefly  on  crude 
differences  in  physical  properties."79 
Proteins  can  be  carried  out  from  solution  by  other  colloids  (i.  e., 
mastic  or  ferric  hydroxide),  and  upon  this  property  methods  have 
been  founded  for  separating  proteins  from  solution.80  The  reaction 
is  not  always  reversible,  in  that  the  protein  cannot  always  be  dis- 
solved out  from  the  precipitate  by  water.  Certain  proteins  can  also 
be  removed  from  solution  by  solid  substances,  which  act  as  ab- 
sorbents, such  as  precipitated  silicic  acid,  meerschaum,  etc.  From 
certain  globulin  solutions  of  about  2-3  pro  m.,  the  following  ab- 
sorbents take  the  following  percentages  :81 
Meerschaum   100  BaSOi   26 
Precipitated  Si02   100  CaS04   18 
Iron  oxide    97  S   2-3 
Kaolin    64 
Serpentin    53 
This  absorption  is  possibly  a  question  of  electro-chemical  affinity. 
Proteins  can  usually  be  precipitated  from  solution  by  means  of 
neutral  salts.    "  If  a  salt  be  added  to  a  mixture  of  proteins,  as  soon 
76  D.  R.  P.  K.,  Vol.  30,  p.  13757,  June  21,  1902. 
77  Banzhaf,  E.  J.,  Johns  Hopkins  Hosp.  Bull.,  Vol.  22,  p.  106,  1911. 
78  Brieger,  L.-,  Festschrift  f.  R.  Koch.,  p.  445,  1903. 
79  Schryver,  S.  B.,  in  Thorpe,  E.,  "  Dictionary  of  Applied  Chemistry," 
Vol.  4,  p.  407. 
80Rona,  P.,  and  -Michaelis,  L.,  Biochem.  Zeits.,  Vol.  5,  p.  365,  1907;  Vol. 
2,  p.  219,  1906. 
81  Landsteiner,  K.,  in  Kolle,  W.,  and  v.  Wassermann,  A.,  "  Handbuch  d. 
Mikroorganismen,"  Vol.  2,  pt.  1,  p.  1246. 
