556 
NOTES  ON  PLASMA. 
have  both  recorded  this  fact  against  plasma,  and  it  is  difficult  to 
discredit  anything  advanced  by  observers  of  so  large  experience 
and  of  such  well  known  carefulness.  But  without  intending  any 
contradiction  of  the  observations  of  others,  I  am  bound  to  as- 
sert that  I  never  saw  a  particle  of  mould  upon  plasma,  and  that 
since  1858  I  have  never  been  more  than  a  few  days  at  a  time 
without  plasma  in  stock.  It  is  possible  the  mould  to  which 
these  gentlemen  refer  may  have  appeared  upon  some  of  the 
compound  plasmas.  I  admit  I  have  not  kept  many  of  these  for 
any  length  of  time,  but  such  as  I  have  kept — Plasma  Unci  and 
Plasma  petrolei — have  remained  as  free  from  mould  as  simple 
plasma  itself.  I  do  not  therefore  feel  disposed,  as  yet,  to  admit 
"a  disposition  to  become  mouldy  by  keeping  "  as  a  proved  fact 
against  plasma  ;  but,  on  the  other  hand,  am  bold  to  assert  that 
it  has  the  but  one  weak  point  already  admitted. 
Though  I  have  prepared  plasma  in  batches  varying  from  one 
ounce  to  twenty  pounds,  and  have  for  experimental  purposes  occa- 
sionally modified  my  formula,  I  have  found  no  advantage  to  result 
from  any  change,  either  in  the  proportions  of  the  ingredients  or 
in  the  selection  of  any  particular  starch  granule.  Some  experi- 
mentalists have  supposed  considerable  differences  in  the  results 
to  have  attended  the  employment  of  different  feculas.  My  own 
experience  goes  rather  to  constrain  me  to  attribute  all  variations 
of  result  to  slightly  altered  manipulation.  For  instance,  if? 
after  heating  the  mixed  ingredients  to  the  required  temperature 
and  for  the  required  time,  the  vessel  be  removed  from  the  fire 
and  its  contents  allowed  to  cool  without  further  stirring,  they 
will  become  gelatinous  and  toughly  elastic,  a  consistence  very  in- 
convenient for  the  required  purpose,  but  by  a  little  judicious  stir- 
ring during  the  process  of  cooling  this  may  be  entirely  obviated, 
and  an  excellent  ointment-like  consistence  obtained.  Again,  I 
have  observed  the  translucency  of  the  result  to  depend  a  good 
deal  upon  the  time  the  mixture  is  exposed  to  heat,  and  the 
amount  of  stirring  during  the  last  part  of  the  process.  I  find 
arrowroot,  tous-les-mois,  and  potato  starch  will  all  give  equally 
good  results  under  exactly  similar  circumstances ;  and,  on  the 
other  hand,  they  all,  under  slightly  modified  circumstances,  will 
yield  inferior  results. 
