MATERIA  MEDICA  OF  THE  INTERNATIONAL  EXHIBITION.  547 
branches  of  Eucalyptus  viminalis  La  Bill.  The  exudation, 
which  is  said  to  result  from  the  punctures  of  insects,  takes  place 
most  copiously  in  the  early  part  of  summer,  at  which  time  the 
manna  appears  as  a  translucent  liquid,  resembling  thin  honey, 
and  gradually  solidifies.  This  Australian  manna  has  net  hith- 
erto been  collected  for  medicinal  purposes. 
3.  Australian  Insect-Manna  called  Lerp. — Having  only 
recently  obtained  a  specimen  of  this  substance  which  to  me  was 
previously  unknown,  I  am  unable  to  offer  much  information 
respecting  it.  According  to  the  Victorian  Exhibition  Report 
published  at  Melbourne  this  year,  we  find  that  the  leaves  of 
Eucalyptus  dumosa  Cunn.,  called  by  the  colonists  Mallee  Scrub, 
becomes  coated  at  certain'seasons  of  the  year  with  an  opaque 
white  saccharine  substance  in  such  profusion,  that  the  shrubby 
vegetation  has  the  appearance  of  being  iced.-  This  substance, 
which  among  the  aborigines  of  the  northern  districts  of  the  col- 
ony obtains  the  name  of  lerp,  is  the  secretion  of  an  insect  of  the 
Psylla  family,  and  consists  (judging  from  the  specimen  in  my 
possession)  of  a  series  of  depressed  hemispherical  cells,  each 
from  a  tenth  to  a  sixth  of  an  inch  in  diameter,  placed  contigu- 
ous to  each  other,  and  adhering  together  so  as  to  form  irregular 
flakes,  sometimes  an  inch  or  more  across.  These  cells  are  com- 
posed of  a  semitransparent,  colorless,  or  yellowish  substance, 
which  is  somewhat  smooth  in  their  interior,  but  which  on  their 
external  surface  forms  transparent  woolly  filaments,  so  closely 
interwoven  that  the  outer  surface  of  a  flake  shows  no  evidence 
of  the  cellular  structure  beneath.  Each  cell  is  the  habitat  of 
an  insect,  which  when  fully  developed,  escapes  by  boring  a  pas- 
sage through  the  top  of  the  cell  to  the  outer  air. 
The  Lerp  manna  has  an  odor  resembling  manna  of  the  ash, 
a  similar  color  and  the  same  clammy  feeling  to  the  touch  ;  it 
has  a  saccharine  taste,  but  does  not  dissolve  in  the  mouth.  It 
is  not  wholly  soluble  in  cold  water  or  in  cold  alcohol ;  boiled  in 
water,  it  breaks  down  so  as  to  form  a  turbid  mucilaginous 
liquid,  which  is  colored  intensely  blue  upon  the  addition  of 
iodine.  Like  the  Australian  manna  previously  noticed,  the 
Lerp  manna  has  not  at  present  any  useful  application. 
4,  Alhagi  Manna  has  been  sent  to  the  Exhibition  from 
India.    It  is  a  saccharine  substance  in  small,  loose,  dry  grains 
