362  Insect  Powders  of  Commerce.  {^mi™l'vmvm' 
taken  into  consideration.  Although  the  paper  itself  was  thus 
limited  in  scope,  the  discussion  which  followed  covered  the  whole 
ground.  Mr.  Robinson  expressed  his  incredulity  at  the  presence  of 
any  toxic  agent,  but  this  bold  skeptic  was  crushed  by  the  President, 
assisted  by  Mr.  Howie  and  Mr.  Martindale. 
In  the  Pharm.  Zeitschr.  fur  Russland,  1890,  E.  Hirschsohn  states 
that  the  active  principle  is  neither  a  volatile  oil  nor  an  acid  resin ; 
this  statement  is  neutralized  by  F.  Schlagdenhauffen  in  an  article  in 
the  Pharm.  Zeitung,  1892,  in  which  he  states  that  he  found  the 
toxic  properties  to  be  (a)  yellow  volatile  oil,  and  (b)  uncrystallizable 
soft  resinous  mass,  pyrethrotoxic  acid  very  soluble  in  ether.  It 
seems  to  me  that  the  average  buyer  of  insect  powder,  after  careful 
consideration  of  the  foregoing  evidence  by  so  many  able  men,  would 
remain  more  or  less  doubtful  as  to  the  properties  and  characteristics 
for  which  he  ought  to  look  in  deciding  upon  the  value  of  the  various 
qualities  to  be  found  in  the  insect  powders  of  commerce.  The 
results  of  my  own  work  on  this  part  of  the  subject  may  be  briefly 
stated  as  follows : 
The  toxic  properties  are  due  to — 
[a)  A  volatile  oil  amounting  to  0  5  per  cent,  in  picked  specimens 
of  closed  flowers,  and  much  less  in  open  flowers. 
(b)  A  soft  acid  resinous  body,  this  is  the  principal  source  of  the 
toxic  effect.  It  is  found  to  the  amount  of  4  8  per  cent,  in  selected 
closed  flowers,  less  than  4  per  cent,  in  half  open  flowers,  and  still 
less1  in  flowers  that  are  fully  open ;  the  whole  plant,  apart  from  the 
flowers,  contains  mere  traces  of  resin. 
The  fine  dry  powder,  after  exhaustion  with  ether,  has  no  decided 
toxic  properties,  but  numerous  experiments  on  beetles  convince  me 
that  this  exceedingly  fine  powder  contributes  something  to  the 
insecticidal  properties  by  its  physical  action,  perhaps  by  its  effect  on 
respiration,  reducing  the  vitality  of  the  insect,  and  also  by  impeding 
locomotion,  and  preventing  a  speedy  retreat  from  noxious  surround- 
ings, and  a  safe  return  to  the  customary  lodgings.  The  toxic  proper- 
ties of  the  volatile  oil  and  resin  may  be  proved  by  isolating  them 
and  mixing  them  with  an  inert  powder,  whose  physically  deterrent 
equation  has  been  ascertained  by  experiment  on  beetles.  I  believe 
no  vivisection  license  is  required  for  this. 
Having  referred  to  the  toxic  constituents  of,  and  the  proportions 
in  which  they  exist  in,  genuine  powder  of  the  flowers  of  C.  cinerarise- 
