group,  though  not  resistant  against  Diazo-colouring  matters,  as 
trypanred,  and  arsenic  compounds  and  vice  versa.  Mesnil’s 
observation  contradicts  to  a  certain  extent  this  statement,  as  a  strain 
lesistant  against  Atoxyl  was  found  to  be  influenced  by  Orsudan. 
Ehrhch* * * §  explains  this  complex  phenomenon  on  the  assumption 
that  the  avidity  of  the  arseno-receptors  of  the  trypanosomes  for 
arsenyl  has  diminished  to  such  an  extent,  that  the  protoplasm  of  the 
trypanosomes  has  become  unable  to  combine  with  the  Atoxyl. 
The  fact  that  an  Atoxyl-resistant  strain  is  still  influenced  by 
arseno-phenyl-glycine  seemingly  contradicts  his  conception.  The 
interpretation  which  Ehrlich  gives,  is  that  although  the  trypanosomes 
of  an  Atoxyl-resistant  strain  have  lost  the  greater  part  of  the  avidity 
of  their  arseno-receptors  for  Atoxyl,  yet  enough  still  remains  to 
permit  of  the  action  of  arseno-phenyl-glycine  being  manifested. 
In  the  hands  of  one  of  us  an  Atoxyl-resistant  strain  in  mice,  sent 
by  Piofessoi  Ehihchi"  early  in  ipoy,  was  shown  to  lose  its  resistance- 
against  Atoxyl  when  inoculated  into  rats. 
Independently,  Mesnil  and  Brimont^  came  to  a  similar 
conclusion,  que  la  race  est  resistante  a  I’Atoxyl  dans  un  org'anisme 
donne.’ 
Breinl  and  Nierenstem,§  m  their  work  with  an  Atoxyl-resistant 
strain  of  T.  briicei  in  donkeys,  were  able  to  prove  that  the  acquired 
resistance  against  Atoxyl  only  holds  good  for  a  given  species  of 
animal,  and  that  this  acquired  character  is  retained  for  this  given 
species  even  after  prolonged  passages  through  different  animals  in 
which  parasites  are  not  resistant.  On  subinoculation  of  the  Atoxyl- 
resistant  parasites  into  rats,  only  in  the  first  generation  was  a  slight 
resistance  noticeable.  In  the  second  generation  the  parasites 
behaved  in  the  same  way  as  .the  normal  control  strain.  Mesnil  ‘and 
Brimont*!!  find  that  an  Atoxyl-resistant  strain  in  mice  is  still  influenced 
to  a  certain  degree  by  Asodyl,  very  slightly  by  trisulphide  of  arsenic. 
Whether  arsenious  acid  still  effects  Atoxyl-resistant  trypanosomes  or 
*  Ehrlich.  Verhandlungen  der  deutschen  derniatologischen  Gesellschaft,  X, 
(  ongress,  1908. 
t  Ehrlich.  Jour,  of  the  Roy.  Inst,  of  Public  Health,  Vol.  XX,  No.  7,  p.  391. 
:  Mesnil  et  Brimont.  Comptes  Rendus  de  la  Soc.  de  Biol.,  Tome  LXIV,  1008 
P-  637.  ^ 
§  Breinl  and  Nierenstein.  Deutsche  med.  Wochenschrift,  No.  27,  1908. 
H  Mesnil  et  Brimont.  Annales  de  ITnstit  Pasteur,  Tome  XXII,  p.  856,  1908. 
