Am.  Jour.  Pharm. 
Sept.  1919. 
Colloidal  Metals. 
627 
as  gelatin  or  gum,  and  the  subsequent  removal  by  dialysis  of  the 
by-products. 
The  great  difficulty  which  attended  the  use  of  electrically-pre- 
pared colloids  on  their  introduction  was  their  instability.  The 
particles  had  a  natural  tendency  to  agglutination,  and,  in  conse- 
quence, the  solution  did  not  remain  therapeutically  active  for  more 
than  a  few  hours.  The  usual  methods  of  preservation  appeared  to 
be  useless.  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 
solution  at  once  agglutinated,  and  any  therapeutic  action  was  conse- 
quently nullified.  It  was  found,  however,  that  the  introduction  of  a 
small  proportion  of  another  colloid,  such  as  gelatin  or  gum,  pre- 
vented this  agglutination,  and  the  addition  of  such  substance,  known 
as  a  "protective  colloid,"  has  allowed  of  these  preparations  being 
preserved  and  isotonized  for  therapeutic  use. 
For  a  time  it  was  thought  that  the  therapeutic  action  of  these 
colloidal  solutions  was  merely  catalytic  or  mechanical,  but  it  is  be- 
lieved now  that  other  factors  are  responsible.  The  results  recorded 
of  colloidal  sulphur  in  the  treatment  of  rheumatism;  of  colloidal 
silver  in  gonorrhoea ;  of  colloidal  antimony  in  kalaazar,  all  point  to 
an  intensification  of  the  specific  action  of  the  metal,  which  is  prob- 
ably in  the  ionic  condition.  Be  that  as  it  may,  the  fact  remains  that 
whereas  it  was  originally  thought,  and  probably  with  some  reason  in 
the  case  of  Bredig's  solutions,  that  the  actual  metal  employed  was 
immaterial,  it  is  now  known  that  the  different  colloidal  metals  have 
different  therapeutic  effects,  and  cannot  be  employed  indiscrimi- 
nately. 
Of  the  chemically  produced  colloids  the  principal  are  arsenic, 
antimony,  copper  ("cuprase"),  gold,  iodine,  iron,  mercury,  plati- 
num, selenium,  silver,  sulphur.  "  Oscols  "  and  "  collosols  "  are 
chemically  prepared  colloids,  the  names  being  the  property  of  cer- 
tain manufacturers. 
Electrically  produced  colloids  include  copper,  gold,  mercury, 
selenium,  silver,  etc.  The  products  on  the  market  are  styled 
"electr-," — thus  electragol  (silver);  electraurol  (gold). 
Under  the  name  of  "  organosols,"  Martindale  describes  colloidal 
metals  obtained  by  impregnation  of  lanolin  with  an  aqueous  solu- 
tion of  the  salt  of  a  heavy  metal,  and  subsequent  trituration  with  a 
