DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE.  435 
prophylactics  and  as  curative  agents,  in  diseases  caused  by 
blood-poisoning :  in  Dr.  De  Ricci's  words,  they  neutralize  the 
zymotic  principle — the  ferment — without  being  injurious  to  life. 
33.  The  Tar  Acids  (carbolic  and  cresylic  acids.) — These 
two  bodies  are  so  commonly  known  under  the  name  of  acids, 
that  I  shall  continue  so  to  designate  them,  although  by  chemists 
they  are  more  generally  classed  with  the  alcohols.  They  have 
great  similarity,  and  only  within  the  last  few  months  have  they 
been  met  with  separately  in  commerce,  having  hitherto  been 
both  called  carbolic  acid.  Creosote,  ^f«v,  to  preserve  flesh,) 
prepared  from  coal  tar,  one  of  the  most  powerful  antiseptics 
known,  was  thought  to  be  impure  carbolic  acid,  until  1854,  when 
Professor  Williamson  and  Mr.  Fairlie,  in  an  investigation  of  it, 
discovered  that  it  was  a  mixture  of  carbolic  and  cresylic  acids. 
It  was  then  taken  for  granted  that  Reichenbach's  creosote,  from 
wood  tar,  had  a  similar  composition,  until  Hlasiwetz,  in  1858, 
showed  that  this  creosote  was  a  different  body  from  carbolic  or 
cresylic  acids.  Finally  Dr.  Hugo  Muller,  in  1846,  discovered 
that  true  creosote  and  its  analogue  guaiacol  belonged  to  a  differ- 
ent class  of  bodies,  and  consisted  of  methyl-oxy-phenic  and 
methyl-oxy-cresylic  acids.  No  experiments  on  the  large  scale 
have  yet  been  tried  with  true  creosote,  as  I  have  only  been  aware 
within  the  last  few  weeks  that  this  compound  could  be  obtained' 
in  quantity. 
Pure  carbolic  acid  is  a  white  crystalline  solid,  melting  at 
34°  C,  and  distilled  at  180°  C. ;  a  trace  of  water  or  oily  im- 
purity renders  it  liquid,  and  for  disinfecting  purposes  it  is 
always  supplied  in  this  form,  to  avoid  the  extra  expense  and 
trouble  needed  for  the  separation  of  the  last  traces  of  impurity ; 
cresylic  acid  is  liquid,  it  boils  at  203°  C,  and  closely  resembles 
carbolic  acid  in  odor  and  other  properties.  Before  the  com- 
mencement of  these  inquiries  it  was  thought  to  be  of  little  or  no> 
value  as  a  disinfectant,  but  Dr.  Angus  Smith  has  lately  shown 
that  it  rivals,  if  it  does  not  surpass,  carbolic  acid  in  antiseptic 
properties.  For  the  present  purpose  of  cattle  plague  disinfection 
it  is  immaterial  which  acid  is  used,  and  to  avoid  unnecessary 
repetition  I  shall  use  the  term  carbolic  acid  to  express  either 
acid,  or  the  commercial  mixture  of  the  two  acids. 
