320 
Disinfection. 
Am.  Jour.  Pliarrti. 
July,  1915. 
Another  writer  attempts  to  throw  a  veil  of  mystery  over  them  by 
assigning  them  to  the  class  of  diphenyls. 
For  the  purpose  of  this  article  the  composition  and  structure  of 
those  high  coefficient  oils  are  unimportant.  The  sanitarian  is  more 
concerned  with  the  efficiency  of  the  disinfectant  prepared  from  them. 
Is  there  real  value  in  it  in  proportion  to  the  claimed  efficiency?  Can 
confidence  be  placed  in  the  statement  of  its  value  when  this  so  far 
exceeds  that  of  phenol  and  similar  disinfectants?  The  question  may 
also  suggest  itself,  How  is  it  possible  that  a  product  less  toxic  and 
less  corrosive  than  carbolic  acid,  practically  harmless  when  diluted 
as  it  can  and  should  be  before  using,  is  so  exceptionally  active  that 
bacteria  are  killed  in  dilutions  fifteen  to  twenty  times  as  great  as  can 
be  safely  recommended  for  phenol? 
The  average  user  of  a  disinfectant  rarely  knows  from  results 
whether  it  is  efficient  or  not,  because  he  has  neither  the  facilities  nor 
the  skill  to  test  it,  and  because  incomplete  disinfection  or  entire  ab- 
sence of  it  may  not  be  followed  by  any  infection  directly  traceable  to 
such  a  failure.  Even  the  chemist,  however  familiar  he  may  be  with 
disinfectant  oils,  cannot  determine  with  certainty  the  efficiency  of  any 
product  entirely  by  its  chemical  properties.  Bacteriological  rather 
than  chemical  control  is,  therefore,  a  very  essential  requirement  for 
disinfectants.  Hygienic  measures  are  too  vitally  important  to  be  open 
to  suspicion  regarding  the  substances  used.  The  methods  of  applying 
them  are  so  often  open  to  question  that  the  substances  must  be  in 
the  highest  degree  efficient. 
The  ideal  disinfectant  has  been  described  in  great  detail  by  differ- 
ent authors.  But  the  ideal  disinfectant  for  every  kind  of  disinfection 
is  probably  unattainable  and  its  desirability  questionable. 
Formaldehyde,  mercuric  chloride,  silver  nitrate,  phenol,  and  the 
coal-tar  derivatives  each  has  its  sphere  of  usefulness,  and  each  is  more 
or  less  ideal  in  that  sphere.  Where  a  coal-tar  derivative  is  applicable, 
however,  there  are  certain  properties  possessed  by  this  class  of  high 
coefficient  disinfectants  which  very  closely  approach  the  ideal  for 
general  disinfection. 
The  average  coal-tar  disinfectant  of  Group  2  is  used  in  a  solution 
of  one  per  cent.,  in  which  dilution  it  is  about  as  efficient  as  a  three 
to  five  per  cent,  solution  of  phenol.  One  of  the  disinfectants  of 
Group  3,  with  a  phenol  coefficient  of  20  when  diluted  to  a  one  per 
cent,  solution,  is  four  times  as  efficient  as  a  five  per  cent,  solution  of 
carbolic  acid  crystals.    The  accompanying  chart  is  a  graphic  repre- 
