422  Keratin  and  Keratinized  Pills.  {A\l°^7m™' 
der  this  form  are  rather  numerous.  Among  them  may  be  men- 
tioned : 
(1)  Medicines  that  can  by  prolonged  contact  cause  irritation  to  the 
mucous  membrane  of  the  stomach  :  arsenic,  salicylic  acid,  creasote, 
chrysarobin,  quinine  compounds,  copaiba  balsam,  cubebs,  ferruginous 
preparations  and  especially  perchloride  of  iron,  opium,  mercurial 
preparations  and  especially  biniodide  and  bichloride  of  mercury,  phos- 
phorus and  all  the  tsenifuge  preparations. 
(2)  Medicines  that  can  injure  the  digestion  by  giving  insoluble 
precipitates  with  pepsin  and  peptones  :  tannin,  alum,  acetate  of  lead, 
preparations  of  bismuth,  nitrate  of  silver,  corrosive  sublimate,  etc. 
(3)  Medicines  that  are  rendered  inactive  or  decomposed  by  the 
gastric  juice  :  alkali,  bile,  soap,  sulphide  of  calcium,  sulphide  of  iron, 
pancreatin,  etc. 
(4)  Medicines  which  should  arrive  in  the  intestines  as  concentrated 
as  possible :  kousso,  santonin,  extract  of  male  fern,  alkali. 
For  the  preparation  of  a  solution  of  keratin  suitable  for  the  coating 
of  pills  several  formula?  have  been  proposed,  in  all  of  which  either 
acetic  acid  or  ammonia  figures  as  a  solvent.  As,  however,  certain 
medicines  are  modified  or  decomposed  by  one  or  other  of  these 
substances,  a  choice  of  formula  should  be  made  according  to  circum- 
stances. For  instance,  the  acetic  solution  might  be  used  for  coating 
pills  containing  salts  of  mercury,  gold  or  iron,  arsenic,  creasote,  sali- 
cylic acid,  tannin,  alum,  etc.  On  the  other  hand,  an  ammoniacal 
solution  might  be  had  recourse  to  for  pills  containing  pancreatin, 
trypsin,  bile,  alkalies,  sulphide  of  iron,  etc.  For  certain  other  sub- 
stances, such  as  naphthaline,  it  is  immaterial  which  of  the  solutions  is 
used. 
Keratin  is  prepared  by  Unna  by  steeping  parings  of  horn  in  a 
digestive  liquid  composed  of  pepsin,  1  gram,  hydrochloric  acid,  1 
gram,  and  water,  11  grams,  as  long  as  the  shavings  yield  anything  to 
the  solvent.  The  residue  is  then  dissolved  in  ammonia  by  maceration 
lasting  several  weeks,  after  which  the  solution  is  evaporated. 
Gissmann  boils  the  quills  of  birds'  feathers  in  glacial  acetic  acid  for 
twenty-four  to  thirty-six  hours  in  a  retort  furnished  with  a  return 
condenser.  A  thick  yellow-brown  liquid  is  thus  obtained,  which  is 
filtered  through  glass  wool,  evaporated  on  a  water-bath  to  the  consis- 
tence of  an  extract  and  afterwards  dried. 
Dieterich  employs  Gissmann's  process,  but  before  the  treatment  with 
