AnMi?ch,f902.rm'}         Animal  Digestive  Ferments.  117 
have  naturally  been  a  scientific  and  practical  advance  in  contrast  to 
the  reliance  upon  fluids  containing  little  or  no  solids,  or  solids  in  an 
indigestible  form. 
The  disastrous  effects  in  the  past  of  delusive  ideas  as  to  what 
constituted  food  for  the  sick  have  been  seen  in  the  dependence  so 
largely  placed  upon  beef  tea  and  extracts  containing  purely  stimu- 
lating nitrogenous  bodies.  The  effect  produced  upon  animals 
in  feeding  them  upon  pure  gelatin,  or  protein,  or  sugar,  only  con- 
firms experience  and  reason  as  to  the  futility  of  such  experiments 
in  determining  the  value  of  foods,  for  if  we  were  to  measure  the 
value  of  food  elements  by  such  results,  we  should  logically  have  to 
conclude  that  no  element  is  suitable  for  nutrition. 
It  is  here  interesting  to  mention  that  we  are  now  obliged  to 
qualify  the  view  once  so  generally  accepted  as  to  the  absolutely 
innutritive  quality  of  gelatin.  Recent  physiological  investigations 
go  to  show  that  gelatin  in  the  ordinary  diet  exerts  a  marked  influ- 
ence in  conserving  and  promoting  the  energy  of  other  protein 
compounds,  and  probably  in  the  building  up  or  the  replacing  of 
the  connective  tissues  analogous  to  gelatin. 
At  the  outset  of  this  paper  the  writer  referred  to  the  far-reaching 
scope  of  the  subject.  It  will  be  seen  that  from  whatever  direction 
we  approach  the  physiological  and  pharmacological  investigations 
involved,  we  find  matter  of  scientific  and  practical  interest,  and 
embodied  in  voluminous  literature.  Reference  even  to  these 
researches  has  only  been  possible  by  restricting  ourselves  to  those 
points  of  the  greatest  practical  purport. 
It  is  evident  that  we  have  arrived  at  a  position  where  we  can  deal 
with  the  enzymes  in  pharmacy  and  medicine  with  as  much  practical 
certainty  as  with  drugs  and  chemicals.  It  is  true  that  we  do  not 
know  what  pepsin  is:  but  if  we  ever  succeed  in  isolating  the  enzymes, 
in  order  to  prove  for  them  a  peculiar  chemical  constitution,  it  is  not 
easy  to  see  how  we  shall  thereby  make  advance  in  pharmacy  or 
medicine.  Inasmuch  as  we  do  not  know  the  chemical  constitution 
of  the  enzymes;  have  no  chemical  tests  or  reagents  to  distinguish 
them  as  a  group  or  as  individuals,  or,  as  it  is  often  expressed,  "  we 
know  the  digestive  ferments  only  by  their  action,"  this  is  often  inter- 
preted or  stated  from  the  viewpoint  of  presenting  a  distinct  limita- 
tion and  defect  in  our  knowledge.  But  the  physiological  test  quite 
transcends  in  delicacy  the  chemical,  for  it  enables  us  to  get  the  char- 
