by  the  volume  of  business,  but  by  the  question  whether  any  particular
charge  to  an  individual  dealing  with  him  is,  considering  the  service
rendered,  an  unreasonable  exaction. In  other  words,  if  he  has  a  thousand
transactions  a  day  and  his  charges  in  each  are  but  a  reasonable  com-
pensation for  the  benefit  received  by  the  party  dealing  with  him,  such
charges  do  not  become  unreasonable  because  by  reason  of  the  midtitude
the  aggregate  of  his  profits  is  large. The  question  is  not  how  much  he
makes  out  of  his  volume  of  business,  but  whether  in  each  particular
transaction  the  charge  is  an  unreasonable  exaction  for  the  services  ren-
dered. He  has  a  right  to  do  business. He  has  a  right  to  charge  for  each
separate  service  that  which  is  reasonable  compensation  therefor,  and  the
legislature  may  not  deny  him  such  reasonable  compensation,  and  may  not
interfere  simply  because  out  of  the  multitude  of  his  transactions  the
amount  of  his  profits  is  large. Such  was  the  rule  of  the  common  law
even  in  respect  to  those  engaged  in  a  quasi  public  service  independent
of  legislative  action. In  any  action  to  recover  for  an  excessive  charge,
prior  to  all  legislative  action,  who  ever  knew  of  an  inquiiy  as  to  the
amount  of  the  total  profits  of  the  party  making  the  charge?  Was  not
the  inquiry  always  limited  to  the  particular  charge,  and  whether  that
charge  was  an  unreasonable  exaction  for  the  services  rendered?"

This  rule  is  amply  established  by  the  authorities  as  well  as  by
economic  considerations. While  the  rule  is  clear^  it  is  necessarily
flexible. It  is  impossible  to  deduce  a  mathematical  fonnula
through  which  it  may  be  applied. The  cost  of  rendering  the
service  may  be  determined  with  reasonable  accuracy. Its  value
in  dollars  is  not  susceptible  of  the  same  measurement^  but  may  be
ascertained  with  sufficient  accuracy. There  is  no  hard  and  fast
line  showing  just  where  the  rates  should  fall  to  equitably  divide
the  spread  between  the  cost  of  the  service  and  its  value,  as
between  the  utility  and  its  patron. What  is  the  proper  line  is  not
an  arithmetical  question. It  is  an  economic  question. Its  solu-
tion demands  the  exercise  of  sound  trained  judgment. The  ques-
tion arises  as  to  each  specific  rate,  and  is  whether  that  rate  is
equitable  as  between  the  utility  and  the  class  of  patrons  to  which
it  applies. 