4^7 
THE  REGULARITY  OF  THE  TIME  OF  REAPPEARANCE 
OF  PARASITES  AFTER  TREATMENT 
It  IS  a  w6ll-known  fact  that  after  the  injection  of  a  trypanocide  in 
experimental  trypanosomiasis  the  parasites  disappear.  If  the  treat¬ 
ment  is  then  discontinued,  the  parasites  usually  reappear  after  a 
variable  period.  In  our  large  experience  with  T.  ga^nbiense  and 
T.  brucei  we  have  been  able  to  observe  that,  to  a  certain  extent,  a 
regularity  prevails  in  the  interval  between  disappearance  and 
reappearance.  In  infection  with  T .  gambiense  in  rats  and  monkeys, 
this  interval  usually  extends  over  fifty  to  sixty  days  after  injection  of 
Atoxyl  or  Orsudan  and  discontinuance  of  treatment.  In  infections 
with  T.  br2icei  in  rats,  guinea-pigs  and  dogs,  on  the  other  hand,  only 
sixteen  to  twenty-five  days  elapse  before  reappearance.  This  is  a 
very  interesting  observation,  for  which  we  are  at  present  unable  to 
account.  It  suggests  that  Atoxyl  may  be  retained  in  the  organism  for 
such  a  period,  and  that  only  after  its  entire  removal,  the  multiplication 
of  the  very  few  surviving  parasites  sets  in  anew.  This  discrepancy 
between  the  relapsing  time  after  infection  with  T.  brucei  and 
T.  gambiense  may  be  due  to  a  slower  multiplication  of  the  latter 
parasite  in  comparison  with  the  former.  In  our  therapeutical  experi¬ 
ments  with  p-  and  m-ammo-phenyl-stibinic  acid  the  relapsing  time 
did  not  generally  show  the  same  regularity. 
It  is  possible,  on  the  other  hand,  that  the  course  of  the  relapses  is 
determined  by  the  life-history  of  the  trypanosome.  Breinl  and  his 
co-workers  were  able  to  work  out  a  life-history  of  T.  gambiense  m 
the  warm-blooded  host,  but  after  prolonged  research  were  unable  to 
observe  any  life  cycle  of  T.  brucei,  and  could  only  demonstrate 
multiplication  by  simple  fission.  This  observation  makes  it  doubtful 
if  the  regularity  of  relapsing  time  can  be  dependent  upon  a  definite 
life  cycle. 
VALUE  OF  SUBINOCULATIONS 
Particular  stress  has  been  attributed  to  the  value  of  submoculation 
of  peripheral  blood  from  an  animal  after  treatment,  in  order  to  decide 
whether  the  animal  has  been  cured  from  the  disease.  In  our  opinion, 
no  conclusion  concerning  a  definite  cure  can  be  drawn  from  sub¬ 
inoculation.  If  subinoculations  are  made  shortly  after  injections  of  a 
