They  found  that  after  continuation  of  the  treatment  for  some  time 
the  drug-  had  no  effect  upon  the  parasites. 
Franke*  found,  ‘working  with  mice  infected  with  Ngana  and 
treated  with  parafuchsin,  that  when  the  recurrences  ceased  to  respond 
to  the  treatment,  inoculation  into  fresh  animals  gave  rise  to  an 
infection  which  was  from  the  very  beginning  uninfluenced  by 
parafuchsin,  administered  either  by  feeding  or  by  injection.’ 
Browmngt  then  observed  a  similar  behaviour  of  certain  trypano¬ 
some  strains  against  Atoxyl. 
It  was,  however,  Ehrlich  who  first  recognised  the  general 
importance  of  this  phenomenon,  and  drew  attention  to  the  fact  that 
one  can  produce  strains  resistant  to  all  types  of  trypanocides.  He 
had  at  his  disposal  strains  resistant  against — (i)  Atoxyl,  (2)  Trypan- 
red,  (3)  Trypanblue,  (4)  Atoxyl  and  trypanblue,  (5)  Arseno-phenyl- 
glycine,  (6)  Tartar  emetic.+ 
Ehrlich  was  further  able  to  prove  that  this  resistance  may  be 
preserved  throughout  many  passages  in  mice,  and  he  regards  this 
feature  as  einen  schonen  Beweis  fiir  die  Vererbung  erworbener 
Eigenschaft.’  However,  in  the  case  of  one  strain  (Atoxyl  strain. 
No.  i),  which  kept  resistant  for  six  months  (67  passages),  this 
acquiied  chaiacter  was  lost  after  seven  and  three-quarter  months 
(87  passages).  A  striking  characteristic  of  the  resistance  is  its  specific 
natuie,  i.e.,  if  a  strain  has  become  resistant  to  parafuchsin  it  is 
resistant  as  well  against  all  colouring  matters  of  the  tri-phenyl-methan 
*  Quoted  by  C.  H.  Browning.  Journal  of  Path,  and  Bacteriology,  Vol.  XII, 
1908,  p.  176.  ’ 
t  Ehrlich.  Berl.  klin.  Wochenschrift,  No.  9-12,  1907.  Reprint,  p.  22. 
^  Strains  of  trypanasomes  resistant  to  tartar  emetic  have  also  been  obtained  by 
:vlesnil  and  Bnmont,  by  Plimmer  and  Bateman  ;  and  a  strain  of  T.  briicei  resistant 
against  p-amino-phenyl-stibmic  acid  has  been  obtained  by  us.  This  resistance 
however,  was  not  transmissible  on  subinoculation.  Mesnil  and  Brimont  succeeded 
m  obtaining  a  permanent  antimony  resistant  strain  by  treating  an  Atoxyl-resistant 
strain  with  antimony.  At  first  the  parasites  were  influenced  by  tartar  emetic,  but 
after  the  fifth  injection  they  became  resistant,  a  resistance  which  persisted  for 
seventy-six  passages. 
observed  by  us  when  treating  guinea-pigs 
W  ^  J'  Orsudan.  After  six  to  seven  injections  the  dmg 
had  lost  its  influence  on  the  parasites.  ° 
Uhlenhuth  Hiibner  and  Woithe,  working  with  T.  equiferdum,  were  not  able 
to  confirm  entirely  Ehrlich  s  observations.  They  were  only  able  to  produce  a 
Atoxjd  influenced  the  parasites  in  a  normal  way.  Therefore,  they  regard  it  as  a 
oMhTteTm  ^  it  an  ab.solute  resistance  in^Ehrlicb’s  sense 
