578  Colloid  Preparations  in  Medicine.      { iugus?Y92o: 
Shortly  after  the  introduction  of  collargol,  Trillet  succeeded  in 
preparing  derivatives  of  certain  metals  by  precipitating  solutions  of 
metallic  salts  with  an  alkali  in  presence  of  albumin,  forming  a  kind 
of  colloidal  sols  of  the  metals.  Later,  Bredig  produced  true  colloidal 
"sols"  of  the  metals  by  passing  an  electric  current  through  pure 
water  between  electrodes  of  the  metal  to  be  dissolved.  The  current 
diffuses  a  minute  quantity  of  the  metal  throughout  the  liquid — the 
metal,  in  fact,  becomes  volatilized  in  the  liquid.  The  resulting  sol 
is  in  every  case  a  dichroic  liquid,  transparent  to  transmitted  light 
and  opaque  to  reflected  light.  The  suspended  particles  in  a  properly 
prepared  Bredig  colloidal  sol  are  so  minute  that  they  can  be  detected 
only  by  the  ultra-microscope,  and  they  possess  the  vibratory  motion 
known  as  "Brownian  movement." 
The  early  literature  concerning  the  therapeutic  action  of  these 
liquids  was  practically  confined  to  France.  A.  Robin  was  the  pioneer 
student  in  this  field.  He  compared  the  sols  of  Bredig  first  to  organic 
enzymes  and  then  later  to  antitoxic  serums.  He  is  enthusiastic 
as  to  their  possibilities  and  describes  wonderful  effects  obtained  from 
them  in  the  treatment  of  pneumonia,  articular  rheumatism,  puer- 
peral infections,  meningitis,  etc.  The  great  difficulty  attending 
the  use  of  electrically  prepared  colloidal  metals  was  their  unstable- 
ness.  The  particles  had  a  natural  tendency  to  agglutinate  and  in 
consequence  the  solution  did  not  remain  therapeutically  active  for 
more  than  a  few  hours.  Sterilization  by  heat  caused  the  particles 
to  agglutinate  and  the  same  result  followed  the  addition  of  a  foreign 
substance  such  as  sodium  chloride.  When  injected  into  the  blood,, 
the  colloidal  sol  at  once  agglutinated  and  any  therapeutic  action 
was  consequently  nullified.  It  was  found  that  the  introduction  of 
a  small  portion  of  another  colloid  such  as  gelatin  or  gum,  at  a  suit- 
able stage  in  the  manufacture,  prevented  this  agglutination  and  the 
addition  of  such  a  substance  known  as  a  "protective  colloid"  has 
allowed  of  these  preparations  being  preserved  and  isotonized,  and 
this  discovery  made  colloidal  metals  a  commercial  as  well  as  a  thera- 
peutic possibility. 
Electrically  prepared  colloidal  sols  are  not  stable  enough  for 
therapeutic  purposes,  so  that  the  methods  now  generally  employed 
are  chemical  ones  and  in  the  case  of  a  metallic  colloid  consist  in  the 
reduction  of  the  metallic  salt  by  a  suitable  agent  in  the  presence  of  a 
protective  colloid  such  as  gelatin  or  gum.  The  metal  is  produced 
in  a  very  fine  state  of  subdivision  and  is  kept  in  this  condition  by 
the  protective  colloid,  the  by-products  are  removed  by  dialysis. 
