AmNo°vUri92iarm' \  Chemical  Elements  of  Living  Matter.  747 
dominant  function  as  the  substance  endowing  complexity,  variability 
and  individuality  to  organic  compounds. 
2.  Hydrogen,  constituent  of  water  and  present  in  all  acids  and 
bases,  plays  an  important  role  in  biochemical  reactions.  Free  hydro- 
gen gas,  a  mild  reducing  agent,  is  formed  as  fermentation  product 
and  occurs  in  the  intestinal  gases  of  mammals,  the  result  of  bacterial 
composition  of  the  carbohydrates : 
Composition  of  Intestinal  Gases  (Ruge) 
ioo  volumes  contain  No  CO 2  CH± 
in  vegetable  diet        1-4  10-19  2I_34  44~55 
in  meat  diet              1-3  45-64  8-13  26-37 
in  milk  diet             43~54  36-38  9-16  i~2 
Many  biochemical  reactions  are  due  to  the  formation  of  water  or 
neutralization  H  +  OH  =  H20.  Free  acids  or  H+  (hydrogen 
ions)  are  of  importance  in  gastric  digestion  and  animal  respiration. 
Bases  or  hydroxy!  ions  (OH—)  occur  in  the  saliva  and  other  secre- 
tions. The  splitting  off  of  water  takes  the  place  in  the  synthesis 
of  carbohydrates  while  the  taking  up  of  water  occurs  in  the  hydro- 
lysis or  breaking  down  of  the  carbohydrates.  To  the  great  affinity 
of  hydrogen  for  oxygen,  many  other  reactions  must  be  ascribed 
which  involve  the  dissociation  and  separation  of  oxygen  from  vari- 
ous compounds.  Hydrogen,  therefore,  is  the  active  principle  in  the 
cell  metabolism  which  is  readily  oxidized,  and  performs  the  service 
of  a  reducing  agent. 
3.  Oxygen,  the  great  oxidizer,  circulates  in  the  cell-organism  as 
the  releaser  of  energy, — it  is  the  energy  carrier  of  life  furnishing 
heat  and  power  to  the  living  machines.  Both  hydrogen  and  oxygen 
are,  as  water,  the  principal  constituent  of  protoplasm, — without 
water  there  could  be  no  cell-life.  But  free  oxygen  is  the  great  sus- 
tainer  of  life,  it  is  absorbed  by  the  blood  of  animals,  and  carried 
to  every  cell  in  need  of  it,  yielding  by  its  reactivity  heat  and  energy. 
Composition  of  the  Gases  of  Blood 
100  vol.  blood  contain  O2         N%  C02 
of  arterial  blood  18  2  40 
of  venous  blood  12  2  48 
Oxygen  is  not  only  the  most  abundant,  but  also  the  most  important 
element  and  its  discovery  laid  the  foundation  of  modern  chemistry. 
