ON  PEPSINE. 
265 
its  solution  becomes  slightly  turbid,  and  loses  entirely  its  digest- 
ive properties. 
There  has  been  considerable  difference  of  opinion  with  regard 
to  the  nature  of  the  acid  in  the  natural  gastric  juice ;  some 
Chemists  assert,  that  the  acidity  is  mainly  due  to  hydrochloric 
acid,  some  are  advocates  for  phosphoric  acid,  others  again  for 
lactic  acid,  but  it  is  universally  admitted  that  the  gastric  juice 
must  be  acid,  to  produce  its  physiological  effects,  and  that  lactic 
acid  is  always  present  to  a  greater  or  less  extent.  Lehmann 
found,  that  when  gastric  juice  is  distilled,  the  first  portions  which 
passed  over  were  free  from  hydrochloric  acid,  but  as  the  liquid 
became  more  concentrated,  hydrochloric  acid  was  obtained;  and 
this  he  ascribed  to  the  property  possessed  by  concentrated  lactic 
acid  of  decomposing  the  compounds  of  the  strongest  acids,  and 
in  this  case  to  the  decomposition  of  the  chloride  of  sodium. 
In  order  to  determine  this  question,  M.  Boudault  made  the 
following  experiments.  He  first  wished  to  ascertain  whether 
the  gastric  juice,  as  it  issued  from  the  mucous  membrane,  was 
acid  or  not.  With  this  view,  the  rennet-bags  were  carefully 
cleaned  and  washed  as  long  as  any  acid  reaction  was  manifested 
to  litmus  paper ;  the  cells  were  then  bruised,  and  treated  with 
cold  distilled  water ;  and  in  this  way  a  perfectly  neutral  fluid 
was  obtained.  This  fluid  did  not  possess  the  power  of  digesting 
fibrine  at  the  temperature  of  the  body,  but  on  the  addition  of  a 
little  lactic  acid  a  complete  digestion  was  obtained. 
Now  it  is  well  known  that  pepsine  has  the  property  of  con- 
verting glucose  or  grape  sugar  into  lactic  acid,  and  when  we 
consider  that  the  saliva  can  by  its  action  convert  amylaceous 
substances  into  glucose,  and  that  pepsine  determines  the  con- 
version of  glucose  into  lactic  acid,  we  have  a  very  fair  explana- 
tion of  the  acidity  of  the  fluid  found  in  the  stomach. 
Boudault  found  that  a  mixture  of  glucose,  neutral  pepsine,  and 
fibrine,  yielded  complete  digestion  after  twelve  hours.  The  pro- 
cess of  digestion  did  not,  however,  commence  until  the  liquid  had 
assumed  a  strongly  acid  reaction.  I  will  not,  however,  say  that 
lactic  acid  is  the  only  acid  which  is  capable  of  playing  this  part; 
on  the  contrary,  hydrochloric  and  acetic  acids  yield  perfect  di- 
gestions, but  not  with  the  same  rapidity  as  lactic  acid. 
From  a  number  of  digestive  experiments  carefully  performed, 
