590  Valuation  of  Drugs  and  Foods.      {ADe'cemt»e£ its™" 
pepo.  For  details  of  the  manner  of  study  see  Heald's  paper.  Suffi- 
cient is  it  to  say  that  the  roots  of  the  germinating  seeds,  when 
about  20  millimetres  long,  are  marked  at  a  distance  of  15  milli- 
metres from  the  top  by  means  of  a  fine  brush  and  India  ink.  They 
are  then  held  in  perforations  in  a  cork  so  that  the  root  is  immersed 
in  the  liquid  of  desired  concentration  and  substance.  Growth 
of  seedlings  is  allowed  to  take  place  in  a  dark  chamber  with  a 
nearly  uniform  temperature  (21  to  230  C).  At  the  end  of  twenty- 
four  hours  the  seedlings  are  removed  and  measured  again.  The 
roots  are  also  examined  for  other  symptoms  of  poisoning,  besides 
the  retardation  or  inhibition  of  growth.  They  are  then  replaced 
for  another  twenty-four  hours,  when  measurements  are  again  made. 
The  solutions  of  the  various  concentrations  of  different  substances 
produce  varying  results.  In  the  more  concentrated  solutions 
growth  may  not  take  place  at  all.  In  the  more  dilute  solutions 
growth  may  be  very  rapid.  In  some  cases  there  is  a  diminution  in 
size  of  the  root. 
These  writers  have  experimented  with  a  large  number  of  inor- 
ganic substances,  and  recently  True  and  Humkle1  have  extended 
this  method  of  study  to  that  class  of  organic  bodies  known  as 
phenols.  They  experimented  with  germinating  seeds  of  Lupinus 
albus  and  Spirogyra  with  the  following  substances: 
Phenol;  phenol  -J--  1  NaOH  ;  pyrocatechol ;  resorcinol ;  resorcinol 
-f-  iNaOH;  hydroquinone;  pyrogallol;  phloroglucin ;  ortho-cresol ; 
ortho-cresol  -f  iNaOH  ;  meta-cresol;  meta-cresol  -f  iNaOH  ;  para- 
cresol;  para-cresol  -f  iNaOH;  carvacrol;  carvacrol  -f  iNaOH; 
thymol ;  thymol  +  I  NaOH  ;  orcinol  ;  ortho-nitrophenol;  ortho-nitro- 
phenol  -j-  1  NaOH;  para-nitrophenol;  para-nitrophenol  -f-  1  NaOH ; 
nitrobenzine ;  tri-nitrophenol  (picric  acid) ;  sodium  picrate  ;  anisol ; 
guaiacol ;  ortho-oxy-benzoic  acid;  sodium  salicylate;  methyl  salicy- 
late. 
As  a  result  of  their  work,  they  found  that,  "  except  in  isolated 
instances,  electrolytic  dissociation  plays  but  a  very  subordinate 
role  in  determining  the  toxic  properties  of  substances.  Picric  and 
salicylic  acids  strongly  dissociate  and  become  powerfully  poisonous, 
by  virtue  of  the  H  ions,  in  great  measure.  Pyrogallol  and,  probably, 
methyl  salicylate,  first  undergo  other  molecular  changes,  after  which 
lBot.  Centralbl.,  No.  1898,  48-51. 
