128 
Glycerin  in  Astringents,  etc. 
f  Am.  Jour.  Pharm. 
t     Mar.  1, 1874. 
thought  that,  whether  applied  externally  or  taken  internally,  these 
remedies  have  a  more  or  less  local  action,  producing  astriction  or  cor- 
rugation of  the  tissues,  or  coagulation  of  the  fluids.  In  regard  to 
tannic  acid,*  Pereira  says  "  Tannin  acts  on  the  animal  tissues  by  vir- 
tue of  its  affinity  for  their  constituents.  It  forms,  with  albumen  and 
gelatine,  compounds  which  are  insoluble  in  water,  and  it  also  com- 
bines with  fibrin;  when  taken  into  the  stomach  it  unites  with  the  con- 
stituents of  the  epithelium,  and  of  the  mucous  membrane  of  the  ali- 
mentary canal."  It  may  therefore  be  assumed  that  astringents  are 
in  general  merely  chemical  agents,  and,  if  their  anticipated  effect 
is  to  be  realized,  their  chemical  composition  must  not  be  modified  or 
disturbed. 
In  order  to  determine  the  chemical  action  of  glycerin  on  astrin- 
gents I  have  commenced  a  series  of  experiments,  wThich  has,  so  far, 
only  been  completed  so  as  to  afford  indications  of  a  definite  and  sat- 
isfactory conclusion.  The  substance  chosen  as  best  representing  the 
class  of  vegetable  astringents  is  gallo- tannic  acid — the  tannin  ©f 
commerce ;  the  mineral  astringents  may  be  aptly  represented  by  the 
perchloride  and  persulphate  of  iron. 
The  effect  of  reagents  on  an  aqueous  solution  of  the  glycerinum  acidi 
tannici  is  precisely  similar  to  that  produced  on  a  simple  aqueous  solu- 
tion of  tannin.  The  salts  of  iron,  tartrate  of  potash  and  antimony, 
chloride  of  sodium,  sulphuric  and  hydrochloric  acids,  and  gelatin, 
give,  in  both  cases,  colorations  and  precipitates,  alike  in  appearance. 
In  order  to  ascertain  the  comparative  power  of  the  two  solutions  in 
precipitating  gelatin,  solutions  equal  in  tannin  strength  were  prepared, 
and  it  was  found  that  an  equal  number  of  measures  of  the  same  so- 
lution of  gelatin  were  required  for  precipitation. 
Being  unable  to  detect  any  difference  in  the  behaviour  of  these 
aqueous  solutions,  a  solution  of  tannin  in  glycerin,  undiluted,  was 
treated  with  solution  of  gelatin,  and  it  was  found  that  the  tannin  was 
not  precipitated ;  or,  at  least,  that  only  a  small  portion  of  the  glycerin 
solution  which  was  in  immediate  contact  with  the  water  contained  in 
the  solution  of  gelatin  was  so  affected.  This  superficial  layer  of  co- 
agulum  was,  on  the  application  of  a  gentle  heat,  immediately  dissolved. 
This  result  is,  so  far,  satisfactory,  and  affords  a  possible  explanation 
of  the  fact  before  alluded  to — that,  in  order  to  realize  the  full  astrin- 
*  Elements  of  Materia  Medica  and  Therapeutics,  Yol.  i.,  p.  98. 
