ON  THE  ODORS  OF  PERFUMES. 
77 
M.  Chevreul  proposes  to  define  odors  by  means  of  a  scale, 
analogous  to  our  notation  of  sounds,  or  for  gradations  of  color 
by  the  chromatic  diagram  (which  last  device  we  also  owe  to  this 
savant).  The  great  obstacle  to  this  plan  is  the  difficulty  of  em- 
ploying the  sense  of  smell  as  we  employ  that  of  sight  or  hear- 
ing, a  difficulty  much  increased  by  the  toleration  which  the 
smell  soon  acquires  to  odors — becoming  <  blase.* 
In  1830  he  endeavored  to  take  account  of  the  changing  odors 
exhaled  by  the  woad  vats  during  evaporation,  if  possible  to  de- 
fine exactly  the  kind  of  color  appropriate  to  each  condition  of 
the  vat.  He  reached  no  positive  results,  although  he  detected 
in  the  dye  stuff  bath  five  perfectly  distinct  odors  ;  the  odor  of 
ammonia,  a  sulphurous  odor,  a  metallic  odor,  an  aromatic  odor, 
clinging  for  many  months  to  the  wooden  stuffs  which  had  passed 
through  the  woad  vat,  and  lastly,  the  odor  of  a  volatile  acid 
analogous  to  that  of  animal  matters  in  decomposition.  M. 
Chevreul  hoped  to  detect  in  these  odors  of  the  dye  vats  symp- 
toms to  guide  the  dyer  in  his  art,  as  the  physician  finds  new  in- 
dications in  his  knowledge  of  symptoms  depending  on  the  chemi- 
cal nature  of  organic  solids  and  liquids,  if  these  symptoms  can 
be  certainly  recognized  by  their  odor.  Thus  he  did  not  shrink 
from  exposing  himself  to  the  most  repulsive  odors  of  the  organ- 
ism to  reach  his  results.  Having  often  heard  the  odor  of  a  can- 
cer spoken  of  as  characteristic  he  examined  it  and  recognized  it 
to  be  a  compound  of — 1st,  an  ammoniacal  odor  turning  blue  a  red- 
dened test  paper.  2d,  a  feeble  butyric  odor.  3d,  a  heavy  odor 
which  is  familiar  in  the  <  trying  out '  of  suet  or  lard.  No  spe- 
cific odor  exists  then  in  cancers,  since  the  three  odors  recognized 
coexist  in  non-cancerous  matters  which  the  disease  alters.  He 
recognized  these  matters  in  the  odor  of  pus  and  other  products 
of  animal  origin,  and  he  also  detected  in  them  a  sulphurous  odor 
and  a  smell  of  fish,  due  probably  to  a  compound  ammonia. 
To  all  these  odors  he  adds  what  he  calls  the  stale-nauseous 
(fade  nauseabonde)  which  appears  in  well-water  that  has  atood 
/  some  days  in  a  vessel  in  which  have  been  placed  egg  shells  im- 
pregnated with  albumen. 
[We  may  be  permitted  to  add  to  these  interesting  facts  some 
others  which  we  submit  to  the  distinguished  author  of  the  chro- 
matic circle  and  researches  on  the  fatty  bodies. 
