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INTRODUCTION 
riie  ease  witii  which  infection  caused  by  the  different  pathogenic 
Liypanosonies  can  be  transmitted  from  animal  to  animal,  and 
especially  the  fatality  of  such  infection  in  small  laboratory  animals, 
has  attracted  the  attention  of  many  workers. 
I  he  action  of  various  compounds  which  are  chemically  allied  has 
been  studied  with  the  object  of  finding  an  absolute  cure  for  different 
Irj'panosome  infections.  1  his  would  obviously  be  of  the  utmost 
economic  importance  in  different  jiarts  of  the  tropics. 
Efforts  in  this  direction  have  led  to  great  progress  in  our 
Iviiowledge  of  the  biology  of  tryiianosomes  ;  they  have  thrown  much 
light  on  protozoal  diseases  m  general ;  they  have  advanced  our 
experience  in  experimental  chemotherapeutics,  and  have  opened  up  a 
new  and  large  field  for  original  investigation. 
1  he  large  number  of  drugs  of  specific  trypanocidal  character  can 
be  classified  into  three  distinct  groups.  To  the  first  group  belong 
compounds  containing  as  their  active  principle  arsenic  in  an  inorganic 
form,  such  as  Sodium  arsenate  ;  to  the  second,  those  in  which  the 
arsenic  molecule  is  masked  by  different  organic  radicals,  such  as  the 
aniline  nucleus,  in  Atoxyl  and  numerous  allied  compounds.  To  this 
second  group  also  belong  the  different  colouring  matters  of  the  diazo 
type  :  trypanred,  trypanblue,  and  derivatives  of  the  triphenylmethan 
type,  such  as  malachite  green,  parafuchsin  and  tryparosan.  The  third 
group  consists  of  Antimony  in  the  form  of  sodium  antimonyl  tartrate 
and  in  the  form  of  the  three  isomeric  arylstibinic  acids. 
ORGANIC  ARSENIC  COMPOUNDS 
A.  Atoxyl. 
Shortly  after  the  discovery  of  the  therapeutic  value  of  Atoxyl  in 
experimental  f  lypanosomiasis,  this  drug  was  extensively  studied, 
it  has  been  applied  in  the  treatment  of  Sleeping  Sickness  and  natural 
trypanosome  infection  in  cattle,  with  very  varying  results.  The 
mechanism  of  its  action  has  been  carefully  studied,  and  Atoxyl  may 
be  regarded  at  present  as  one  of  the  best  known  drugs. 
riiomas  and  Breinl*  first  introduced  Atoxyl  into  the  treatment  of 
*  (a)  Ihoraas.  British  Medical  Journal,  May,  1905. 
(^)  Ihomas  and  Breinl.  Liverpool  School  of  Tropical  Medicine,  Memoir 
\VI,  1905, 
