Am.  Jour.  Pharm.) 
Mar.,  :2;8.  J 
Dialysis, 
103 
a  galvanic  battery  ;  but  is  it  necessary,  in  order  that  diffusion  shall 
occur,  that  the  septum  or  membrane  shall  be  porous  ?  Not  in  the 
ordinary  acceptation  of  the  term,  at  least,  as  diffusion  or  dialysis  takes 
place  most  rapidly  through  structureless  basement  animal  membrane, 
where,  with  the  most  carefully -corrected  objective,  we  are  unable  with 
the  highest  powers  of  a  microscope  to  differentiate  a  single  stoma  ;  or, 
as  perhaps  a  more  simple  instance,  we  may  take  Lhermite's  experiment 
in  illustration,  viz.  :  A  tube  was  partly  filled  with  chloroform,  upon 
this  was  poured  a  column  of  water,  and  above  this  was  placed  a  column 
of  ether.  After  standing  a  short  time,  the  ether  had  passed  entirely 
through  the  stratum  of  water  and  become  mixed  with  the  chloroform. 
Or  again,  we  can  illustrate  this  diffusion  through  a  non-porous  septum 
by  taking  a  stratum  of  sulphuric, acid  in  a  tube,  above  it  one  of  water 
and  above  this  a  solution  of  blue  litmus  in  alcohol.  In  a  short  time  the 
litmus  will  be  reddened  through  the  diffusion  of  the  acid  into  the  alco- 
hol. Now,  in  these  experiments  it  is  obvious  that  water  is  not  in  any 
sense  a  porous  medium,  and  hence  we  dismiss  any  theory  having  the 
porosity  of  membranes  as  its  foundation. 
Let  us  now  note  the  various  circumstances  that  modify  or  increase 
this  peculiar  property,  and  primarily  stands  the  fact  that  a  liquid  to 
diffuse  or  dialyze  must  be  capable  of  "  wetting  "  the  interposed  mem- 
brane ;  for,  of  course,  if  the  liquid  is  of  such  nature  that  it  cannot  be 
imbibed  by  the  membrane  no  dialysis  can  occur,  or  if  only  one  liquid 
is  capable  of  wetting  the  membrane,  then  dialysis  will  only  occur  in 
one  direction,  viz.,  from  this  liquid. 
Liquids  to  be  proper  subjects  for  dialysis  should  be  perfectly  misci- 
ble  with  each  other,  or  if  salts,  they  should  be  dissolved  in  a  common 
medium,  and  of  all  media  water  is  the  best.  The  solutions  should  be 
of  different  densities,  though  this  is  not  indispensible,  as  solutions  of 
different  substances  of  the  same  density  will  dialyze  perfectly,  though 
with  less  rapidity. 
Again,  liquids  pass  more  rapidly  through  some  animal  membranes 
from  within  outward,  than  vice  versa,  as,  for  example,  from  the  interior 
of  a  bladder  or  a  stomach  outward,  the  current  being  always  strongest 
on  the  side  presenting  the  epithelial  surface,  but  a  discussion  of  this, 
though  exceedingly  interesting,  is  rather  a  digression  from  the  proper 
subject  of  this  paper. 
The  rate  of  diffusion  is  accelerated  by  a  moderate  increase  of  tem- 
perature, hence  dialysis  is  best  performed  at  a  moderate  temperature. 
