AAuJg°usrt  uS™" \  What  is  an  A ntibody ? 
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are  more  likely  to  arrive  in  good  condition  if  sent  by  parcel  post,  un- 
der present  conditions.  . 
Elder  leaves  are  best  gathered  when  the  green  color  is  fully  de- 
veloped, as  they  are  chiefly  used  for  making  green  oil  ointment,  "01. 
Sambuci  virid." 
Elderberries  for  drying  should  be  collected  as  soon  as  the  berries 
assume  a  reddish-purple  color  or  they  soften  too  much  in  drying.  The 
short  stalks  need  sifting  out  when  they  are  brittle  after  drying. 
For  elderberry  juice  the  ripest  berries  should  be  used,  and  to  the 
juice  i  per  cent,  of  formic  acid  is  added.  The  juice  is  probably  most 
conveniently  obtained  in  country  villages  by  the  use  of  a  cleaned  cider 
press.  The  juice  is  chiefly  used  by  wholesale  manufacturers  of  elder- 
berry wine.  The  formic  acid  can  be  got  rid  of  by  boiling  the  juice 
when  required  for  making  the  wine. 
WHAT  IS  AN  ANTIBODY?* 
Within  the  last  few  years  the  words  "antigen"  and  "antibody" 
have  become  terms  in  the  vocabulary  of  practical  medicine  as  well  as 
in  the  science  of  immunology.  Discussion  of  the  general  phenomena 
of  immunity  can  scarcely  be  carried  on  without  reference  to  them. 
An  antigen  is  a  substance  which,  on  introduction  into  the  body 
in  proper  amounts  and  under  suitable  conditions,  induces  the  forma- 
tion of  a  special  antagonistic  substance,  the  antibody.  At  the  present 
moment  there  are  scarcely  any  well  authenticated  exceptions  to  the 
general  rule  that  every  soluble  complete  protein  may  serve  in  at  least 
some  degree  as  an  antigen.  With  respect  to  the  cleavage  products  of 
the  proteins  the  evidence  of  their  antigenic  properties  is  at  most  de- 
batable; certainly  none  of  the  amino-acids  or  simpler  polypeptids, 
i.  e.,  amino-acid  complexes,  can  serve  as  antigens.  The  alleged  func- 
tion of  lipoids  in  this  role  is  likewise  not  established.  Karsner  and 
Eckert1  insist,  in  fact,  that  if  lipoids  are  obtained  from  animal  tissues, 
favorable  results  may  be  obtained  \  but  in  none  of  these  experiments 
is  it  proved  that  the  lipoids  are  entirely  free  from  proteins.  Far  less 
is  definitely  known  with  respect  to  the  nature  of  the  manifold  anti- 
*From  Jour.  Amer.  Med.  Assoc.,  July  16,  1921. 
1  Karsner,  H.  T.,  and  Ecker,  E.  E. :  The  principles  of  Immunology, 
Philadelphia,  J.  B.  Lippincott  Company,  1921,  p.  22. 
