3H 
Note  on  Plasma. 
(  Am.  Jour.  Pharm, 
\      \  June,  1879. 
of  weight  during  the  second  and  following  weeks  as  compared  with  the 
increase  during  the  first,  owing,  as  I  have  said  to  a  lessening  of  the 
intensity  of  absorption  by  the  presence  of  the  water.  All  this  goes  on 
without  stirring  or  disturbing  the  fluids  in  any  way.  If,  however,  the 
water  be  kept  stirred  into  the  glycerin  instead  of  being  allowed  to  remain 
on  its  surface,  there  will  be  no  appreciable  difference  in  this  increase  of 
weight  between  the  first  and  following  weeks. 
But  at  what  point  is  there  a  pause  in  this  process?  Where  does  it 
end  ?  In  whatever  proportionate  quantity  water  may  be  added  to 
glycerin,  from  a  single  drop  upwards,  absorption  will  take  place  in  a 
moisture-laden  atmosphere  until  the  proportion  reaches  three  parts  by 
measure  of  the  former  to  one  of  the  latter.  At  this  point  the  glycerin, 
so  to  speak,  gives  up  the  contest,  and  succumbs  to  the  influence  which 
the  water  exerts  in  the  opposite  direction.  In  this  mixture,  therefore,, 
namely,  3  fluidounces  of  water  to  I  fluidounce  of  glycerin,  there  will 
be  neither  attraction  nor  evaporation,  the  weight  scarcely  varying  from 
week  to  week  either  in  one  direction  or  the  other. 
If,  now,  we  conduct  our  experiments  in  a  moderately  dry  atmos- 
phere, say  in  the  atmosphere  of  an  ordinary  working  or  sitting-room  in 
which  a  fire  is  kept  burning  during  the  day,  the  action  will  be  the  same, 
but  to  obtain  similar  results  the  proportions  will  be  widely  different,  and 
in  fact  almost  reversed.  Instead  of  3  parts  of  water  to  1  of  glycerin 
we  shall  require  nearly  3  parts  of  gl\cerin  to  1  of  water  to  reach  the 
neutral  point.  Where,  in  one  case,  there  is  absorption  and  augmenta- 
tion, in  the  other  there  is  evaporation  and  consequent  loss;  so  that  in 
order  to  maintain  a  uniform  condition  in  the  mixed  liquids  the  propor- 
tions must  be  adapted  to  the  exact  state  of  the  atmosphere  in  which 
they  are  intended  to  be  kept.  In  a  general  way,  we  may  consider  two 
and  a  half  parts  by  measure  of  glycerin  to  one  of  water  well  adapted  to 
meet  the  end  in  view.  Bearing  in  mind,  then,  that  in  plasma  the  starch 
has  no  effect  in  preventing  the  absorption  of  moisture  (the  mass  being 
by  such  means  gradually  undermined  and  softened  through),  we  take 
advantage  in  preparing  this  substance  of  the  peculiarity  herein  notified, 
and  proceed  accordingly.  Five  fluidounces  of  glycerin  are  mixed  with 
three  fluidounces  of  distilled  water  in  a  porcelain  dish,  or,  preferably, 
transferred  thereto  from  a  vessel  in  which  they  have  been  previously 
well  stirred  or  shaken  together.  The  starch  is  then  added  secundum 
artem,  and  heat  gradually  applied,  with  constant  stirring,  until  a  trans- 
