576  Colloid  Preparations  in  Medicine.      [  iSgus?^9'2'o: 
cess  than  that  of  silver.  The  results  obtained  from  the  use  of 
collosol  manganese  have  likewise  been  little  short  of  astonishing. 
Colloidal  iron  is  of  great  use  in  treating  anaemia  and  chlorosis.  An 
interesting  fact  is  that  it  unites  with  the  amino-acids  of  the  stomach, 
forming  a  compound  from  which  haemoglobin  is  synthesized  in  the 
system.  Colloidal  iodine  has  been  in  use  for  some  time  and  is  toler- 
ably well  known  to  the  practitioner. 
Lastly,  it  is  clearly  to  be  borne  in  mind  that  colloidal  prepara- 
tions are  not  to  be  relied  upon  unless  they  are  fresh.  As  we  said 
above,  the  colloidal  state  is  essentially  unstable;  the  substance  in 
the  form  of  a  colloid  is  precipitated  by  the  particles  of  salt  which 
abound  in  the  atmosphere,  and  even  by  the  minute  quantities  of 
matter  dissolved  from  the  containing  vessel,  as  well  as  by  forces 
at  present  not  clearly  apprehended. 
Coi^ivOiDS  AS  AntisejpTics. — This  is  another  topic  editorially 
commented  upon.  There  is  one  other  property  possessed  by  col- 
loids, however,  which  is  of  direct  medical  interest — their  use  as  anti- 
septics or  germicides.  Bacteria,  physically  considered,  are  colloidal 
in  character,  as  are  the  fluids  in  which  their  life-cycle  is  passed.  All 
colloids — or  rather  the  particles  in  colloid  solution — are  electrically 
charged,  either  positively  or  negatively  as  the  case  may  be.  Most 
substances  bear  the  same  charge  always,  though  there  are  some  col- 
loids which,  if  prepared  in  one  way,  are  negatively  charged,  and  if 
prepared  in  an  alternative  way,  are  positively  charged.  Bacteria 
are  negatively  charged,  hence,  if  in  any  way  it  is  possible  to  neu- 
tralize this  electric  charge  the  bacteria  are  precipitated,  and  are 
thus  removed  from  the  sphere  of  deleterious  action.  The  obvious 
way  to  neutralize  (electrically)  a  negative-  sol  is  to  add,  in  proper 
proportion,  a  positive  sol.  One  can  thus  imagine  the  power  of,  and 
the  convenience  .of  using,  an  antiseptic  which  has  the  following 
properties — that  of  precipitating  bacteria,  that  of  being  chemically 
a  germicide,  and  that  of  being  non-toxic  and  non-caustic.  Such 
would  be  the  properties  of  the  ideal  antiseptic,  and  such  are  the 
properties  of  certain  colloids — those,  namely,  which  bear  a  positive 
charge  and  which  are  also  antiseptic  by  reason  of  their  chemical 
properties. 
The  most  valuable  colloid  by  far,  in  this  connection,  is  colloidal 
silver.  It  has  approximately  the  same  germicidal  action  as  mer- 
curic chloride,  and  in  addition  it  is  non-toxic,  non-caustic,  and  non- 
irritating.    It  has  the  curious  property,  when  injected  intravenously, 
