546  The  Pollen  of  Poison  Sumach.  j^iSSr,1?^ 
known  as  "  ivy  poisoning."  This  vapor  was  believed  to  be  so 
insidious  and  penetrating  that  sensitive  persons  could  easily  be  pois- 
oned by  passing  near  the  emanating  plants  without  touching  them. 
That  the  poisonous  principle  of  this  class  of  plants  is  a  volatile 
substance  appears  to  have  been  the  belief  of  all  of  the  writers  who 
have  treated  the  subject  previous  to  1895.  PfafT  and  his  pupils  1 
then  demonstrated  that  the  poisonous  constituent  of  poison  sumach 
{Rhus  vernix  L.)  and  poison  ivy  (Rhus  toxicodendron  L.)  was  a 
non-volatile,  resin-like  substance.  This  substance,  which  Pfaff*  called 
toxicodendron  was  found  in  nearly  all  parts  of  these  plants.  He 
suggested  that  toxicodendrol  might  be  a  constituent  of  the  pollen 
of  these  plants  and  (since  the  flowers  are  dioecious  and  anema- 
philous)  it  appeared  possible  that  sensitive  persons  might  be  pois- 
oned if  the  pollen  were  blown  upon  the  face  or  hands.    Pfaff  says : 2 
"...  The  activity  of  toxicodendrol  in  minutest  traces  may  make  it 
possible  for  a  few  pollen  grains  of  poison  ivy  to  cause  skin  eruption ;  and 
the  few  cases  of  action  at  a  distance  which  are  so  often  quoted,  may  con- 
cievably  be  thus  explained.  But,  in  my  own  opinion,  it  is  more  than  doubtful 
if  ever  a  case  of  ivy  poisoning  has  occurred  without  direct  contact  with  the 
plant  or  some  article  which  has  been  in  contact  with  the  plant.  The  long 
latent  period  of  the  eruption  in  some  cases  may  obviously  render  mistakes 
extremely  easy  as  to  the  occasion  when  contact  with  the  plant  really  occurred." 
However,  PfafT  did  not  make  any  examination  of  the  pollen  of 
either  poison  ivy  or  poison  sumach  for  toxicodendrol. 
Schwalbe 3  has  stated  the  belief  that  poisoning  without  direct 
contact  with  the  plant  is  easily  possible.  After  a  microscopical  ex- 
amination of  Rhus  diversiloba  T.  &  Gr.  (the  Californian  species  of 
poison  ivy)  he  reported  as  follows : 
"...  There  are  in  the  leaves,  in  the  skin  of  the  stems  and  stalks  of 
the  leaves  and  flowers,  and  even  in  the  petals,  lactiferous  vessels  containing 
the  poisonous  matter  of  the  plant. 
"  Upon  these  vessels  grow  hairs  loaded  more  or  less  with  poisonous 
oil.  These  hairs  are  prevalent  on  the  stems,  on  the  under  surface  of  the 
leaves  and  even  on  the  petals  of  the  plant.  The  hairs  derive  the  poison  by 
osmosis  from  the  laticiferous  vessels  and  are  carried  when  broken  off,  easily 
by  the  wind  or  by  the  help  of  man  or  animals  to  persons  liable  to  the  affection. 
The  presence  of  the  hairs  on  the  stem  during  the  winter,  when  there  are  no 
leaves  on  the  shrub  explains  the  fact  of  the  poisonous  qualities  of  the  plant 
1  Pfaff  and  Orr:  Science,  n.s.  1,  no  (1895). 
2  Jour.  Exp.  Med.,  2,  192  (1897). 
zMed.  Rec,  63,  855  (1903). 
