75o 
Chemical  Elements  of  Living  Matter.  | 
8.  Iron,  the  respiratory  metal  of  animals,  is  present  in  all 
protoplasm  and  is  essential  to  the  formation  of  coloring  matter 
(chlorophyll  of  plants,  haemoglobin  of  animals).  In  haemoglobin  it 
serves  higher  animals  as  an  oxygen  carrier  (i  gm.  Fe  to  150  gm.  of 
red  blood  corpuscles).  The  human  body  contains  about  .005%  iron, 
it  occurs  in  bile,  lymph,  chyle,  gastric  juice,  pigment  of  eye,  milk  and 
in  urine.  Its  most  important  function  is  its  presence  in  haematin 
C34H84N1Fe05  of  the  haemoglobin  which  acts  as  transmitter  of 
oxygen  from  the  lungs  to  the  tissues,  and  of  carbon  dioxide  from 
the  tissues  to  the  lung  (respiration).  It  is  also  invariably  present 
in  the  vegetable  organism: 
Lack  of  iron  leads  to  pathological  chlorosis ;  in  plants  the  leaves  do 
not  seem  able  to  form  chlorophyll,  become  pale  and  unable  to  photo- 
synthesis. 
p.  Potassium,  the  most  electropositive  metal,  is  essential  to 
the  living  tissues  of  plants  and  animals.    It  occurs  in  two  forms: 
(a)  ionized  as  chlorides,  phosphates,  sulphates  and  carbonates,  and 
(b)  masked  in  organic  combination  as  constituent  of  a  large  mole- 
cule. In  the  regulation  of  life  processes  the  potassium  salts  play  an 
important  role  as  stimulating  agents,  acting  on  the  brain,  vaso- 
motoric  and  sensatory  nerves  of  animals.  In  the  plant  organism  it 
is  important  in  the  formation  of  carbohydrates  and  proteins,  for 
without  K  no  starch  is  formed.  Seeds  and  other  organs  rich  in 
proteins  are  usually  rich  in  potassium: 
Content  of  Fe20B  in  the  Ash  of  Plants: 
100  parts  of  ash  contain 
Fe2Oz 
0.8-2% 
0.6-4% 
0.5-1% 
0.5-2% 
in  roots,  average 
in  stems,  average 
in  leaves,  average 
in  seeds,  average 
Comparison  of  Protein  and  Potassium: 
Protein 
100  parts  contain  substance. 
of  dried 
of  ash, . 
Potassium 
Seeds  of  cereals,  average  10.2% 
Seeds  of  legumes,  average  29.0% 
23.07% 
39.2% 
