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C.  Orsudan 
Experiments  on  a  larger  scale  have  been  carried  out  with 
substances  closely  allied  to  Atoxyl,  but  having,  instead  of  an  aniline 
nucleus  (Formula  1),  a  toluidine  nucleus  (Formula  II). 
I.  Sodium  3-methyl  4-amino-phenyl-arsenate  (Kharsin) 
and  its  acetyl  derivativ 
OH 
ONd 
Sodium  3 -methyl  4-acetyl-amino-phenyl-arsenate  (Orsudan). 
After  a  few  preliminary  experiments  the  acetylated  compound 
Orsudan  was  found  to  be  the  less  toxic  of  the  two,  and  most  of  the 
treatment  experiments  were  carried  out  with  it.  It  was  a  remarkable 
fact  that  Orsudan  did  not  have  any  effect  on  rats  or  on  one  donkey 
infected  with  T.  britcei,  although  two  strains  of  this  parasite,  of 
different  origin,  were  used.  On  the  other  hand,  it  acted  promptly  on 
T .  eqiiiperditm  and  T.  gainbiense. 
In  rats  infected  with  T.  eqniperdum,  parasites  disappeared  after 
the  first  injection  of  0’02  5  gm.  of  the  drug,  but  usually  recurrences 
were  observed  after  a  varying  period  if  treatment  was  discontinued. 
Only  a  few  rats  lived  as  long  as  eight  months  without  reappearance 
of  parasites,  but  these  also  succumbed  to  intercurrent  diseases.  Two 
rats  showed  relapses  after  a  very  prolonged  period,  one,  126  days 
after  the  last  injection  of  Orsudan  (0’075  gm.  had  been  administered). 
