4 1 6  Artificial  and  Natural  Digestiojis.  {Am,lug!';i89oarm" 
The  next  series  of  experiments  dealt  with  the  pancreatic  digestion 
of  protei'ds;  here  the  occurrence  of  an  insoluble  bye-product  (anti- 
albumid)  is  believed  to  be  due  to  the  imperfection  of  the  method  of 
artificial  digestion,  and  probably  does  not  occur  in  natural  digestion; 
the  question,  however,  which  was  specially  investigated  was  the 
occurrence  of  leucine  and  tyrosine.  Kuhne  has  already  stated  that 
these  amido-acids  are  formed  in  natural  as  well  as  in  artificial  pan- 
creatic digestion,  but  careful  quantitative  experiments  do  not  seem 
.to  have  been  made,  although  it  may  be  roughly  stated  that  less  of 
these  materials  are  found  in  the  intestines  than  in  a  flask.  This 
may  be  due  to  one  of  two  causes;  either  they  are  normally  formed 
in  large  amount  and  then  rapidly  absorbed,  or  else  they  are  formed 
in  only  small  amount.  By  the  help  of  the  digesting  dialyser,  com- 
bined with  the  examination  of  the  intestinal  contents  of  animals,  it 
was  hoped  in  the  present  research  to  elucidate  this  question.  A  few 
typical  experiments  are  described  in  detail  and  the  following  con- 
clusions drawn :  (i)  The  undigested  residue  in  a  flask  digestion  is 
always  greater  than  that  of  a  dialyser  digestion,  other  conditions 
being  the  same  ;  (2)  the  amount  of  leucine  and  tyrosine  formed  in 
a  flask  digestion  is  always  greater  than  in  a  dialyser  digestion,  other 
conditions  being  the  same.  The  amount  formed  in  a  dialyser  diges- 
tion is,  however,  always  considerable,  and  it  is  possible  that  the 
amount  formed  is  less  than  in  a  flask  digestion,  because  the  peptones 
from  which  they  originate  are  continually  dialysing  out.  Leucine 
and  tyrosine  were  also  found  in  not  inconsiderable  quantities  in  the 
intestines  of  the  animals  examined,  not  merely  in  microscopic 
amounts,  as  some  previous  observers  seem  to  imply. 
The  paper  concludes  with  remarks  of  a  theoretical  nature  on  the 
function  of  the  amido-acids  formed  in  plants  and  in  animals.  It  is 
regarded  as  inconceivable  that  the  animal,  like  the  vegetable  organ- 
ism, should  construct  its  protei'ds  from  the  nitrogen  contained  in  the 
amido-acids,  and  their  importance  is  likened  to  that  of  the  inorganic 
salts  and  extractives  contained  in  beef-tea,  or  other  meat  extract. 
We  do  not  know  what  part  these  play  exactly  in  the  total  processes 
of  tissue-metabolism,  but  we  do  know  that  the  salts  are  in  some  way 
essential,  and  that  the  extractives  are  an  extremely  important  acces- 
sory to  that  metabolism. 
Experiments  on  the  pancreatic  digestion  of  starch  are  in  progress. 
The  term  zymolysis  is  suggested  as  a  .convenient  one  to  denote 
generally  the  changes  produced  by  enzymes  or  unorganized  ferments. 
