4i8 
drug,  even  with  large  quantities  of  blood  into  susceptible  animals,  very 
rarely  do  parasites  appear  in  the  blood  of  the  subinoculated  animal. 
The  result  of  subinoculations  after  a  longer  interval  varies  consider¬ 
ably.  Even  in  the  case  of  large  animals  infeeted  with  T.  brucei,  after 
treatment  and  temporary  disappearance  of  the  parasites,  subinocu¬ 
lations  are  very  frequently  negative ;  sometimes,  hoAvever,  an 
infection  occurs  after  a  very  prolonged  incubation  period. 
Less  reliable  still  are  subinoculations  from  cases  of  Sleeping 
Sickness  patients  into  rats  and  guinea-pigs. 
The  following  is  an  illustration  of  this  statement. 
From  a  patient  in  a  comparatively  early  stage  of  trypanosomiasis, 
at  a  time  when  parasites  eould  be  seen  in  very  small  numbers  in  the 
peripheral  blood,  subinoculations  were  made  into  a  guinea-pig  and 
two  rats.  The  guinea-pig,  although  examined  daily  for  six  months, 
never  became  infected  after  injection  of  2  c.c.  of  blood.  Of  the  two 
rats,  both  showed  parasites  on  very  rare  occasions,  and  then  only  in 
very  scanty  number  (i  to  3  in  each  coverslip  preparation).  One 
showed  i5arasites  on  16  days  out  of  1 1 1  days,  the  other  on  14  days 
out  of  14  months  ;  both  died  from  intercurrent  diseases.  Although 
subinoculations  upon  rats  were  made  from  the  original  rats  on  days 
when  parasites  were  observed,  none  of  the  subinoculated  animals  ever 
became  infeeted. 
WHEN  CAN  AN  ANIMAL  BE  CONSIDERED  TO  BE  CURED? 
Many  statements  have  been  made  concerning  the  efficiency  of 
different  drugs  with  regard  to  the  effect  of  permanent  eures  in 
animals.  One  is  naturally  inclined  to  conclude,  from  a  rapid  and 
apparently  complete  destructive  action  of  arsenic  and  antimony  upon 
tiypanosomes  contained  in  the  blood,  that  the  organism  is  freed  from 
the  parasites.  However,  careful  examination  of  the  blood  after 
treatment  reveals  the  fact  that  only  too  often  parasites  reappear  again, 
even  after  very  prolonged  periods.  We  were  able  with  careful  daily 
examination  to  observe  relapses  in  rats  infected  with  T.  brucei  and 
treated  with  Atoxyl  after  a  negative  period  of  226  days  ;  and  in  rats 
infeeted  with  T.  equiferdum  and  treated  with  Orsudan  as  late  as 
105  and  126  days  after  discontinuation  of  the  treatment. 
