346 
Rhus  Dermatitis. 
Am.  Jour.  Pharm. 
May,  1921. 
RHUS  DERMATITIS.* 
Although  the  toxicology  of  poison  ivy  {Rhus  toxicodendron)  is 
fairly  well  understood,  the  toxic  features  of  the  related  poison  oak 
{Rhus  diver siloba)  have  not  been  studied  to  comparable  extent. 
For  the  harmfulness  of  the  poison  ivy,  Pfaff  1  placed  the  responsi- 
bility on  a  substance  isolated  from  the  plant  and  named  toxicoden- 
drol.  The  latter  is  insoluble  in  water,  but  readily  dissolves  in  the 
organic  solvents  like  ether  and  alcohol.  The  product  is  so  active 
that  0.005  mS-  applied  to  the  skin  may  suffice  to  provoke  local  symp- 
toms with  pain.  A  considerable  latent  period  prior  to  the  appear- 
ance of  the  cutaneous  alterations  has  often  been  described.  Recently 
McNair2  has  come  to  the  conclusion  that  a  polyhydrophenol,  to  which 
the  name  lobinol  has  been  given,  is  responsible  for  the  irritation  of 
the  skin  caused  by  poison  oak.  The  active  substance  isr  neither  bac- 
terial nor  volatile.  Poisoning  occurs  from  actual  contact  with  the 
resinous  sap  of  the  plant;  but,  as  McNair  points  out,  it  may  result 
through  an  intermediary  agent,  which  carries  the  sap,  such  as  par- 
ticles of  soot  in  smoke,  clothing,  cordwood,  croquet  balls,  and  shoes. 
As  in  the  case  of  all  rhus  dermatitis,  the  most  common  avenues  of 
invasion  of  the  poison  are  connected  with  the  cutaneous  surfaces, 
though  the  respiratory  and  alimetary  tracts  may  also  play  a  part  at 
times  in  promoting  intoxication  with  poison  oak.  The  problem  of 
latency  has  not  been  solved.  With  respect  to  the  mechanism  by  which 
the  dermatitis  is  spread  so  that  it  appears  successively  on  different 
areas  of  the  body,  McNair  has  ventured  several  hypotheses.  Thus, 
it  may  be  due  to  (i)lthe  direct  transference  of  the  poison  itself  by 
the  fingernails  or  hands  from  one  part  of  the  J)ody  to<  another,  or  to 
new  areas  from  the  clothes  or  hair;  (2)  reflex  irritation;  (3)  con- 
tiguity of  tissue,  and  (4)  varying  durations  of  latency  for  the  dif- 
ferent skin  surfaces  on  the  body  (varying  with!  the  respective  thick- 
nesses of  their  stratum  corneum,  chemical  and  physical  differences 
in  the  skin,  etc.).  Perhaps  further  study  will  show  an  essential 
identity  in  the  etiology  of  all  forms  of  rhus  dermatitis. 
*  Joum.  Amer.  Med.  Assoc.,  76:  18  (April),  1921. 
1  Pfaff,  F. :  J.  Exper.  Med.  2:  181,  1897. 
2  McNair,  J.  B. ;  ^athology  of  Rhus  Dermatitis,  Arch  Dermat.  &  Syph. 
-3:383  (April),  1921 ;  J.  Am.  Chem.  Soc.  43:i59  (Jan.),  1921 ;  J.  Infect  Dis. 
19:  419  (Sept.),  1916. 
