500  Forms  of  Albumen  in  Urine.  {Am'octu^?.arm" 
mucin,  although  more  slowly  and  less  distinctly  than  does  citric  acid. 
The  degree  of  acidity  of  the  urine  is  probably  an  important  element 
in  relation  to  this  reaction  with  picric  acid ;  and  Professor  Stewart 
thinks  that  where  acid  is  present  in  quantity  the  opalescence  is  dis- 
tinct ;  where  it  is  in  slight  amount,  it  is  comparatively  or  completely 
absent. 
It  is  likely  that  although  picric  acid  often  affects  mucin,  it  does  not 
do  so  in  such  a  way  as  to  render  it  unreliable  as  a  delicate  test  for 
albumen.  Its  precipitate  with  mucin  is,  even  when  applied  by  the 
contact  method,  a  slight,  slowly  developed  haze.  A  precipitate  indi- 
cating albumen  is  more  marked  and  more  quickly  produced-  A  little 
practice  in  the  use  of  the  test  will  soon  render  any  one  familiar  with 
the  degree  and  rate  of  formation  of  the  opacity  which  indicates  albu- 
men as  distinguished  from  those  which  mark  the  presence  of  mucin. 
Potassio-mereurie-iodide,  which  was  first  proposed  as  a  test  by  M. 
Tanret,  corresponds  in  its  action  to  picric  acid,  giving  opacity  with 
serum  albumen,  globulin,  acid  and  alkali  albumen,  and  an  opacity 
dissolved  by  heat  with  peptone  and  propeptone.  But  it  will  be  found 
to  give  a  reaction  with  a  very  large  proportion  of  normal  urines,  and 
as  the  addition  of  an  organic  acid — citric  or  acetic — is  required  to 
bring  out  the  reaction,  it  is  clear  that  mucin  must,  in  many  cases,  give 
a  degree  of  opalescence.  It  may  be  that  other  sources  of  fallacy 
exist  in  regard  to  slighter  reactions.  Dr.  Oliver's  method  of  apply- 
ing this  test  greatly  reduces  the  chances  of  error,  but  its  disadvantages 
render  it  an  inferior  test  to  the  picric  acid. 
Potassium  Ferrocyanide,  first  suggested  by  Dr.  Pavy,  also  resembles 
picric  acid  in  its  action,  except  it  does  not  give  any  indication 
with  peptones.  The  objections  which  induced  Professor  Stewart  to 
reject  the  reagent  last  described  apply  to  this  one  also. 
Dilution  with  water  is  a  convenient  but  not  verv  reliable  test  of  the 
presence  of  serum  globulin,  as  it  produces  a  milkiness,  that  substance 
being  soluble  in  weak  saline  solutions,  but  not  in  pure  water  or 
extremely  diluted  solutions  of  salts.  It  produces  no  effect  upon  other 
forms  of  albumen. 
Magnesium  Sulphate  is  a  valuable  test  for  serum  globulin,  as  it 
produces  a  milky  opacity  with  that  substance,  which  speedily  deposits 
as  a  precipitate.  It  has  no  action  upon  serum  albumen,  peptone  or 
propeptone,  but  produces  an  opacity  with  acid  and  alkali  albumen.  It 
is  best  used  in  saturated  solution  by  the  contact  method.    By  its  use 
