The  Influence  of  Environment        313

action  following  an  alteration  in  the  constitution  of  the

sea  water  is  in  some  of  the  cases  due  to  an  increase  in

the  permeability  of  the  membranes  of  the  cell,  whereby

substances  can  diffuse  into  the  cell  which  when  the

proper    balance    prevails    cannot    diffuse.      For    this

balance  the  ratio  of  the  concentration  of  the  salts  with

univalent  cation  Na  and  K  over  those  with  bivalent

C]\[a_Lj^  salts

cation  Ca  and  Mg     -^ is  of  the  greatest

CCa+Mg  salts  ^

importance.
