﻿THE 
  CRITERIA 
  Ol 
  I.I 
  VI 
  \Ci.\KSS 
  

  

  within 
  its 
  limits. 
  But 
  the 
  ima^e 
  is 
  too 
  ii> 
  n. 
  ral 
  ! 
  1>.- 
  ade- 
  

   quate; 
  we 
  must 
  inquire 
  int> 
  tin- 
  eliaiiiiet'iil 
  integrity 
  "f 
  ili<- 
  

   organism 
  more 
  carefully. 
  Three 
  points 
  are 
  of 
  out.-tandini: 
  

   importance: 
  (a) 
  that 
  the 
  changes 
  in 
  the 
  organism 
  arc 
  very 
  

   complex, 
  having 
  essentially 
  to 
  do 
  with 
  protein 
  substanci 
  - 
  

   in 
  a 
  colloid 
  state; 
  (b) 
  that 
  they 
  are 
  specific 
  for 
  each 
  kind 
  

   of 
  creature, 
  and 
  (c) 
  that 
  they 
  are 
  correlated 
  in 
  such 
  a 
  way 
  

   that 
  they 
  go 
  on, 
  and 
  ttie 
  specific 
  structure 
  likewise 
  persists. 
  

   Let 
  us 
  take 
  each 
  of 
  these 
  points 
  in 
  turn. 
  

  

  (a) 
  Metabolism 
  of 
  Proteins. 
  

  

  According 
  to 
  some 
  physiologists 
  the 
  only 
  absolute 
  differ- 
  

   ence 
  between 
  living 
  organisms 
  and 
  inorganic 
  bodies 
  is, 
  that 
  

   proteins 
  are 
  universally 
  present 
  in 
  the 
  former 
  and 
  absent 
  

   in 
  the 
  latter. 
  \ 
  7 
  erworn 
  writes: 
  " 
  Since 
  it 
  is 
  known 
  that 
  

   the 
  nitrogenous 
  proteids, 
  with 
  their 
  allies, 
  which 
  in 
  part 
  

   are 
  derived 
  from 
  the 
  proteids 
  and 
  in 
  part 
  are 
  necessary 
  to 
  

   their 
  formation, 
  are 
  the 
  sole 
  organic 
  compounds 
  that 
  an 
  

   never 
  wanting 
  in 
  living 
  substance, 
  that 
  everywhere 
  they 
  

   constitute 
  its 
  chief 
  mass 
  and 
  alone 
  are 
  sufficient 
  for 
  its 
  for- 
  

   mation, 
  it 
  can 
  be 
  said 
  that 
  all 
  living 
  organisms 
  are 
  charac- 
  

   terised 
  by 
  the 
  metabolism 
  of 
  proteids' 
  (1899, 
  p. 
  13G). 
  

   These 
  protein 
  compounds, 
  such 
  as 
  white 
  of 
  egg 
  or 
  tin- 
  dut. 
  n 
  

   of 
  bread, 
  are 
  peculiarly 
  intricate, 
  with 
  a 
  large 
  number 
  <>1 
  

   atoms 
  or 
  atom-groups 
  in 
  their 
  molecules; 
  they 
  diffuse 
  very 
  

   slowly 
  and 
  do 
  not 
  readily 
  pass 
  through 
  membranes; 
  th. 
  

   occur 
  in 
  a 
  colloid 
  state, 
  and 
  although 
  some, 
  e.g., 
  haeinoirlnbin. 
  

   are 
  crystallisable, 
  they 
  are 
  not 
  known 
  in 
  a 
  crystalloid 
  state 
  

   in 
  the 
  living 
  organism; 
  they 
  are 
  relatively 
  stable 
  bodi. 
  -. 
  

   yet 
  they 
  are 
  continually 
  breaking 
  down 
  and 
  bein<j 
  built 
  

   up 
  again 
  within 
  the 
  body, 
  partly 
  under 
  the 
  direct 
  influence 
  

   of 
  ferments 
  or 
  enzymes. 
  The 
  constructive, 
  synthetic, 
  up- 
  

  

  