64  The  Function  of  Enzymes.  {Areb^,  m™' 
mentation?  How  do  we  carry  on  those  transformations  of  food 
material  by  which  beefsteak  and  bread  and  butter  at  once  become 
available  sources  of  energy  and  matter  for  our  living  machine  ?  How 
does  a  potato  manufacture  starch  in  its  leaves,  transfer  it  to  the 
growing  tubers,  and  there  store  it  up  for  future  use? 
In  each  case  by  means  of  enzymes,  which  we  may  define  as  the 
tools  of  cells  and  the  reagents  by  which  the  chemical  reactions  of 
cells  of  all  kinds  are  effected. 
The  term  "  ferments  "  was  first  used  early  in  the  nineteenth 
century  by  Schwann  and  Berzelius.  Afterwards  the  word  was  used 
somewhat  indiscriminately,  meaning  either  a  micro-organism  of 
fermentation  or  a  chemical  substance  which  in  some  way  was  re- 
lated to  living  cells.  To  distinguish  between  these,  the  physiologist 
Kiihne  suggested  the  term  "  enzyme  "  to  designate  the  digestive 
ferments  such  as  pepsin,  trypsin,  and  ptyalin.  The  word  has  now 
been  universally  accepted  as  the  name  of  a  group  of  chemical  bodies, 
products  of  living  cells,  which  have  the  peculiar  property  of  effect- 
ing the  chemical  operations  of  living  matter  but  which  do  not  enter 
into  the  final  products  of  these  reactions. 
Chemistry  cannot  produce  enzymes,  for  they  are  found  only  as 
the  products  of  protoplasm  of  living  cells,  and  it  makes  no  difference 
whether  we  are  dealing  with  the  ultra-microscopic  bacterium  or  the 
giant  redwood  or  the  whale,  the  chemical  activities  are  due  to  en- 
zymes. Furthermore,  the  same  kind  of  enzyme  may  be  produced 
by  organisms  of  widely  different  character,  as,  for  example,  the 
trypsin  of  certain  bacteria,  of  the  carnivorous  plants  like  the  Venus 
Fly  Trap,  and  of  the  human  intestinal  tract. 
Since  the  variety  of  chemical  processes  carried  out  by  living  cells 
is  large  in  number,  it  follows  that  the  number  of  enzymes  is  legion. 
Even  the  number  produced  by  a  minute  bacterial  cell  hardly  visible 
with  a  high  power  of  the  microscope  may  be  several,  while  with 
organisms  of  highly  specialized  form  and  physiological  division  of 
labor  the  number  is  greatly  increased.  In  man,  at  least  fourteen 
are  known  to  be  developed  in  the  alimentary  canal,  and  to  take 
part  in  the  process  of  digestion,  while,  if  we  added  all  the  other 
chemical  changes  which  may  be  elaborated  in  the  body  as  a  whole, 
our  catalogue  would  be  greatly  increased.  Moreover,  we  may  assume 
that  there  are  many  enzymes  which  are  still  unknown,  for  the  en- 
zymes may  be  intra-cellular,  that  is,  acting  only  within  the  cell,  as 
well  as  extra-cellular,  or  extruded  outside  the  cell  and  so  possibly 
