ArebJr°uUarr'yTi^2m'}         Animal  Digestive  Ferments.  6 1 
instructive  as  these  investigations  are,  we  cannot  dwell  upon  them 
here. 
In  1883  Kuehne  and  Chittenden  employed  and  advocated  the  use 
of  ammonium  sulphate  as  a  superior  precipitant  of  the  albumoses, 
in  separating  these  from  true  peptone. 
Recent  scientific  inquiry  seems  directed  chiefly  to  attempts  to  iso- 
late the  pure  enzymes  in  the  hope  of  ascertaining  their  chemical 
nature ;  careful  examination  of  the  cleavage  products  of  proteids, 
produced  by  enzyme  or  by  chemical  action,  to  throw  some  light 
upon  the  structure  of  the  proteids  themselves.  Schoumow,  Sima- 
nowski  (1894),  Wroblewski  (1895  and  1898),  Pekelharing  (1896), 
Friedenthal  (1900)  and  Nencki  and  Sieber  (1901)  published  investi- 
gations on  the  chemical  nature  of  enzymes  in  support  of  their  pro- 
teid  nature. 
Chittenden  in  connection  with  his  various  pupils,  Osborne  and 
Campbell,  Hopkins,  Kossel,  Kutscher,  Siegfried  and  others,  have 
since  Kuehne's  time  wrestled  with  the  difficult  problem  of  isolating 
and  characterizing  the  multitude  of  forms  of  proteids,  native  and 
derived,  but  as  yet  the  synthesis  of  albumen  has  not  been  accom- 
plished. 
Chittenden,  chief  among  contemporaneous  investigators  in  phy- 
siological chemistry,  has  made  extended  and  varied  experiments  and 
researches,  and  has  contributed  voluminously  to  the  literature  on 
the  subject.  His  experiments,  in  fact,  are  quite  too  numerous  for 
reference.  We  cite  these  as  especially  pertinent:  "  Human  saliva," 
"  A  comparison  of  natural  and  artificial  gastric  digestion,"  "  Influ- 
ence of  peptones  and  certain  inorganic  salts  on  the  diastasic  action 
of  saliva,"  "  The  relative  formation  of  proteoses  and  peptone  in 
gastric  digestion." 
It  is  also  to  be  said  that  the  studies  of  the  illustrious  Kuehne  are 
likewise  so  voluminous  that  no  adequately  detailed  mention  of  them 
can  be  made. 
New  methods  of  assaying  the  various  preparations  of  digestive 
enzymes  have  been  suggested  by  Kremel,  Mett,  Allen,  etc. 
The  influence,  deleterious  and  beneficial,  of  condiments,  spices, 
beverages,  antiseptics  and  medicinal  agents  upon  the  functions  of 
digestive  enzymes,  received  the  attention  of  Chittenden,  Stutzer, 
Buchner,  Fraser,  Mann,  Mabery,  Goldsmith,  Roberts  and  others. 
Kbnig,  Bomer,  Kjeldahl,   Stutzer,  Wiley,    Mallett,  developed 
