Am.  Jour.  Pharm.  I 
February,  1915.  J 
The  Function  of  Enzymes. 
65 
capable  of  detection.  The  positive  knowledge  of  the  action  of  intra- 
cellular enzymes  is  still  very  meagre,  although  when  Biichner  dis- 
covered zymase  and  a  method  for  its  preparation  in  1897,  the  first 
great  step  forward  in  their  study  was  made. 
What  an  enzyme  really  is,  cannot  be  exactly  stated.  An  enzyme 
is  known  only  by  its  reactions.  "  By  their  works  ye  shall  know 
them,"  is  essentially  true  in  the  ferment  world.  We  cannot  even 
tell  their  composition  or  to  what  class  of  chemical  substances  they 
belong,  for  they  have  never  been  obtained  in  pure  condition.  It  is 
generally  assumed,  however,  without  proof,  that  enzymes  are  protein- 
like in  character.  In  spite  of  this  indefmiteness  and  the  elusive 
character  of  these  bodies,  certain  general  properties  regarding  them 
have  become  known  and  on  these  points  all  enzymes  behave  in  like 
manner,  although  differing  distinctly  from  other  chemical  substances. 
We  may  thus  regard  enzymes  as  forming  a  special  and  peculiar 
group  of  chemical  compounds,  differing  in  certain  ways  from  other 
substances,  and  especially  in  their  relation  to  the  law  of  mass  action 
as  shown  by  the  great  disproportion  between  the  amount  of  the 
active  substance  and  the  amount  of  material  changed.  A  good 
example  of  this  is  rennet,  which,  it  has  been  stated,  can  coagulate 
from  500,000  to  800,000  times  its  weight  of  casein  without  being 
used  up.  All  enzymes  possess  the  same  characteristic  but  not  neces- 
sarily in  the  same  degree.  The  activity  is  largely  dependent  upon 
the  physical  and  chemical  conditions  of  the  environment.  Thus 
very  slight  changes  in  the  reaction  of  the  medium  on  which  an 
enzyme  is  acting  may  control  very  largely  its  power,  or  make  the 
difference  between  high  efficiency  and  practical  inactivity.  Some  en- 
zymes require  neutral  solutions  for  action,  others  are  most  vigorous 
in  slightly  acid  or  slightly  alkaline  media. 
Similarly,  temperature  may  play  a  very  important  part  in  the 
control  of  enzyme  reactions.  In  this  respect,  these  substances  behave 
closely  like  living  cells  and  like  certain  kinds  of  proteins.  Each 
enzyme  has  a  maximum,  a  minimum,  and  an  optimum  temperature 
of  activity,  just  as  microbes  have,  and,  like  these,  if  heated  above  the 
maximum,  will  be  rendered  inactive  and  finally  destroyed.  This 
thermal  death  point,  as  it  may  be  called,  is  very  near  the  coagulating 
point  of  albumin  and  not  far  from  the  death  point  of  most  vegetative 
bacteria.  Another  similarity  to  the  proteins  lies  in  the  fact  that  both 
enzymes  and  albumins  are  precipitated  by  concentrated  salt  solutions 
such  as  ammonium  sulphate,  by  alcohol  and  by  salts  of  heavy  metals. 
