To  a  teased  fresh  preparation  of  liver  in  physiologic  salt  solution  add
a  drop  of  a  5  per  cent,  aqueous  solution  of  acetic  acid.  This  will  cause
the  nucleus  to  appear  more  distinctly.  It  dissolves  also  all  albuminous
granules,  but  leaves  unaltered  fat  and  lipoids.  (This  method  of  treat-
ment may  be  profitably  employed  with  all  fresh  dissociated  (teased)
preparations.  In  the  case  of  the  connective  tissues,  the  acetic  acid  will
cause  the  collagen  fibers  to  swell  and  finally  disintegrate,  but  will  have
no  effect  upon  the  elastic  fibers.)

Subsequently  add  to  the  same  preparation  a  drop  of  a  1  per  cent,
solution  of  methylene  blue.  This  will  stain  the  nucleus  and  thus  cause
it  to  contrast  more  sharply  with  the  cytoplasm.  (Other  equally  good
staining  solutions  for  isolated  tissues  are:  (a)  a  1  per  cent,  solution  of
methyl  green  in  20  per  cent,  alcohol;  (b)  1  per  cent,  aqueous  solution
of  borax  carmin;  (c)  dilute  solution  of  any  of  the  hematoxylin  stains;
(d)  or  a  1  per  cent,  aqueous  solution  of  eosin  may  be  employed  to  stain
the  cytoplasm,  producing  in  this  way  also  a  heightened  contrast  between
nucleus  and  cytoplasm.)

(The  best  way  to  add  any  fluid  to  a  macerated  preparation  under  a
cover-glass  is  to  place  a  few  drops  of  the  solution  at  one  edge  of  the
cover-glass,  and  cause  it  to  flow  under  the  glass  by  withdrawing  fluid
from  the  opposite  edge  by  means  of  blotting  paper.)  Distinguish  be-
tween physical  and  chemical  coloration.
(2)  Sketch  (29)  a  small  area  of  a  stained  section  of  the  liver.
(B)   SQUAMOUS  (Pavement  epithelium).
