chromogenetic  group,  the  arsenical  radical  acts  on  the  parasites  in  the 
same  way  as  a  chromophoric  group  on  a  cotton  fibre,  whereas  the 
serum  plays  the  role  of  a  mordant. 
B.  Derivalives  of  Atoxyl. 
In  order  to  ascertain  whether  certain  derivatives  of  Atoxyl  have  a 
superior  therapeutical  value  in  trypanosome  infections,  a  great 
number  of  compounds  were  experimented  with. 
I.  Acetylated  Atoxyl. 
H  COCK^ 
Acetylated  Atoxyl  was  first  prepared  by  Ehrlich  and  Bertheim. 
It  was  used  by  C.  Browning,  by  Moore,  Nierenstein  and  Todd,  and 
by  Breinl.  It  proved  to  be  less  toxic  for  animals  very  susceptible  to 
Atoxyl,  such  as  dogs,  which,  as  Ehrlich"'  points  out,  is  not  the  case  in 
horses  and  guinea-pigs.  The  only  difference  between  it  and  Atoxyl, 
consists  in  the  partial  acetylation  of  the  amino  group,  which  change 
apparently  reduces  the  toxic  effect  of  the  aniline  nucleus  in  the 
Atoxyl.  Uhlenhuth  and  Woithef  believe  that  the  acetyl  group 
prevents  the  rapid  discharge  of  arsenic,  a  conception  which  is 
improbable.  It  has  been  pointed  out  by  Nierenstein,  that  part  of 
Atoxyl  undergoes  acetylation  in  the  organism,  which  observation 
probably  explains  the  less  toxic  effect  of  acetylated  Atoxyl. 
2.  Salicyli-Atoxyl. 
^N  =  C  Co  H^-OH 
This  compound  was  prepared  with  the  view  of  introducing  Atoxyl 
in  stain  nascendi  into  the  organism,  as  it  might  be  expected  that  on 
Ehrlich.  Berl.  klin.  Wochenschrift,  No.  9-12,  1907.  Reprint,  p.  22. 
t  Uhlenhuth  und  Woithe.  Arb.  aus  dem  Kaisl.  Gesundheitsamte,  Band  XXIX, 
1908.  Reprint,  page  42. 
