164     Chemical  Reactions  of  Diphtheria  Antitoxin.  {  Am'l°rn  ^7™' 
this  solution  was  diluted  to  22  Cc.  Three  Cc.  of  this  dilution  did 
not  protect  against  one  L  -f-  dose  of  the  toxin. 
The  100  Cc.  solution  gave  no  precipitate  with  uranium  acetate 
c.p.,  gold  chloride,  mercuric  chloride,  or  one  half  saturation  with 
ammonium  sulphate,  but  gave  a  slight  precipitate  with  picrolonic 
acid.  Picric  acid  gave  no  precipitate.  This  concentration  gave 
no  biuret  reaction  and  no  test  for  tryptophane  with  magnesium  gly- 
oxalate  and  sulphuric  acid. 
To  see  if  the  last  dilution  was  inactive  owing  to  deterioration,  no 
extra-preservative  having  been  added,  the  original  100  Cc.  was  tested 
4  days  after  its  preparation  and  1  Cc.  still  protected  against  one  L  -f- 
dose  of  the  toxin. 
A  similar  precipitation  was  made  with  a  freshly  prepared  solu- 
tion of  platinum  chloride  (10  per  cent.)  and  the  precipitate  was 
washed  with  NaCl  solution  instead  of  with  distilled  water  as  in  the 
preceding  case.  The  washings  and  centrifugalized  solution  could 
not  be  freed  from  platinum  by  H2S  alone,  even  on  adding  an  excess 
of  platinum,  but  cleared  with  H2S  when  1  Cc.  of  HC1  n/10  was 
added  to  the  solution  (111  Cc).  After  dilution  to  150  Cc.  it  was 
found  that  even  2  Cc.  did  not  protect  against  one  L  +  dose  of  the 
toxin. 
Five  Cc.  of  the  same  antitoxin  was  precipitated  with  a  solution 
of  platinum  chloride  made  2  days  previously.  The  precipitate 
settling  on  centrifugalizing  was  washed  with  distilled  water  as  in 
the  first  experiment  and  after  passing  H2S  became  colorless  save 
for  a  minute  trace  of  golden  color.  This  was  diluted  to  150  Cc 
Even  1  Cc.  protected  against  one  L  +  dose  of  the  toxin. 
From  these  experiments  it  is  evident  that  NaCl  interferes  with 
the  precipitation  of  platinum  unless  acid  is  added. 
There  are  several  ways  of  interpreting  the  activity  of  the  plati- 
num filtrate ;  first,  that  it  contained  the  antitoxin  free  from;  globulin 
or  that  the  acidity,  which  resulted  from  passing  H2S,  weakened  the 
toxin,  or  that  a  trace  of  colloidal  platinum  sulphide  remained  in 
solution  and  weakened  the  toxin. 
The  acidity  of  the  first  platinum  preparation  corresponded  to  0.3 
Cc.  n/10  HC1  to  each  Cc.  The  second,  in  which  much  NaCl  had 
been  used  and  which  was  inactive,  reacted  for  0.55  Cc.  n/10  HC1 
for  each  Cc.  The  third  preparation  which  contained  about  as  many 
antitoxic  units  as  the  first  platinum  preparation,  reacted  for  0.2  Cc. 
n/10  HC1  to  each  Cc. 
