72         ON  CELLULOSE  AND  THE  COMPOSITION  OP  WOOD. 
also  insoluble,  when  purified  as  far  as  possible  from  incrusting 
substances,  and  also  even  when  examined  in  the  young  condition. 
It  therefore  appears  that  the  ligneous  fibres  are  quite  distinct 
from  the  cortical  fibres,  the  latter  being  soluble  in  cuprate  of 
ammonia,  while  the  former  are  insoluble.  That  this  distinction 
cannot  be  accounted  for  by  the  greater  hardness  of  the  woody 
tissue  may  be  inferred  from  the  fact,  that  the  cupro-ammoniacal 
liquor  is  capable  of  readily  dissolving  the  albumen  of  the  Phy- 
telephaSy  or  vegetable  ivory,  which  presents  much  greater  hard- 
ness and  less  porosity  than  the  ligneous  fibres.  M.  Fremy 
sought  to  ascertain  what  the  conditions  are  by  which  the  insol- 
uble tissues  may  be  rendered  soluble.  He  found  that  rice  paper, 
which  is  insoluble  in  the  reagent,  when  submitted  to  the  action 
of  diluted  mineral  acids,  is  converted  into  a  membrane  which  is 
soluble ;  alkalies  also  effect  the  same  result,  but  more  slowly. 
Acetic  acid,  even  boiling,  is  incapable  of  producing  any  change. 
The  ligneous  fibres  and  pith  are  thus  modified  and  converted 
into  the  soluble  condition ;  the  tissue  of  champignons,  however, 
withstand  the  action  of  acids,  and  remain  insoluble.  From  these 
facts  M.  Fremy  concluded  that  M.  Payen,  in  his  endeavor  to 
perfectly  purify  the  tissues,  employed  agents  which  were  capa- 
ble of  modifying  the  principle  itself. 
M.  Payen  has  also  brought  forward  several  experiments  tend- 
ing to  support  his  own  view,  and  contends  that  there  are  not 
sufficient  grounds  for  considering  that  the  insolubility  of  certain 
membranes  in  the  cupric  reagent  is  due  to  the  existence  of  sev- 
eral isomeric  conditions  of  cellulose.  He  states  that  in  all  cases 
the  cellulose,  when  freed  perfectly  from  foreign  matters,  is  sol- 
uble in  the  reagent,  and  that  the  means  employed  in  the  purifi- 
cation are  not  sufficient  to  effect  any  isomeric  modification.  The 
cellular  tissue  of  pith,  he  states,  although  containing  no  incrust- 
ing substance,  is  nevertheless  impregnated  with  certain  bases, 
principally  lime,  which  exist  partly  in  combination  with  silica 
and  partly  with  the  organic  matter.  These  are  so  uniformly 
distributed,  that  after  the  complete  incineration  of  the  organic 
matter  a  white  skeleton  remains,  consisting  principally  of  car- 
bonate of  lime,  of  which  the  weight  amounts  to  6-100ths  of  the 
dried  pith,  and  which,  examined  under  the  microscope,  still  re- 
tain the  form  of  the  tissue.    The  cells  of  the  pith  are,  in  fact, 
