104 
Dialysis. 
(  Am.  Jour.  Pharm. 
\       Mar.,  1878 
To  a  proper  understanding  of  dialysis,  it  is  important  that  all  idea  of 
chemical  action  shall  be  disassociated  from  it.  We  have  before  us  a 
circular  on  Dialyzed  Iron,  stating  that  the  mixed  solution  of  ferric 
chloride  and  oxychloride,  when  brought  into  the  dialysator,  is  decom- 
posed, hydrochloric  acid  passing  through  the  membrane,  leaving  behind 
a  solution  of  ferric  hydrate.  Of  course,  this  is  incorrect,  but  it  is  the 
circulation  of  just  such  statements  which  makes  it  necessary  to  disas- 
sociate all  idea  of  chemical  action  from  dialysis,  as  in  the  instance  above 
quoted  the  ferric  chloride  is  dialyzed,  or  in  other  words,  simply  separ- 
ated from  the  non-dialyzable  ferric  oxychloride,  leaving  the  latter 
remaining  in  the  dialysator. 
All  soluble  substances  may  be  divided  into  two  classes,  viz.,  those  of 
high  diffusive  power,  embracing  nearly  all  those  crystallizable,  which 
are  hence  called  crystalloids,  and  those  of  low  diffusive  power  or  non- 
diffusible,  of  which  albumen  is  a  good  example,  these  being  called 
colloids  ;  these  latter  are  generally  amorphous  in  character. 
This  may  be  exemplified  by  breaking  the  shell  of  an  egg  at  one 
extremity  without  rupturing  the  membrane,  and  inverting  it  in  a  wine- 
glass of  distilled  water.  After  a  few  hours  the  saline  constituents  of 
the  egg  will  have  passed  through  the  membrane,  while  the  albumen 
will  be  found  to  have  passed  through  the  membrane  very  slightly,  if  at 
all.  There  is  obviously  here  no  chemical  reaction  ;  it  is  evidently 
simply  a  separation,  or  in  other  words,  a  true  dialysis.  When  this 
albumen  is  acted  on  by  pepsin  it  is  converted  into  albuminose,  which 
possesses,  curiously  enough,  the  property  of  dialyzing  or  passing  through 
the  membrane  with  extreme  facility. 
Boiled  starch  does  not  dialyze,  while  glucose  dialyzes  very  rapidly, 
hence  starchy  and  albuminoid  food  cannot  dialyze,  or  in  other  words, 
cannot  be  absorbed  until  after  being  digested. 
The  recently-formed  protoplasm  passes  through  the  millions  of  cell 
walls  of  the  ducts  of  plants  by  the  law  governing  dialysis,  the  differ- 
entiated protoplasm  remaining  to  increase  the  cell  walls,  and  the  salts 
and  undifferentiated  protoplasm  passing  through  the  walls  of  the  cells, 
which,  after  all,  are  only  like  so  many  basement  structureless  membranes. 
Salicylic  acid  is  purified  by  passing  through  the  membrane,  the 
gummy  resinous  matter,  which  so  tenaciously  adheres  throughout 
repeated  crystallizations,  is  mostly  removed  by  dialysis,  the  pure  acid 
passing  through  the  membrane  being  separated  or  dialyzed  from  the 
colloid  or  uncrystallizable  contamination. 
