AmkJa°rch.T9w!'m-}     Refined  Methods  in  Water  Purification.  119 
unwound  itself  in  this  fashion:  The  plates  are  of  gelatin;  gelatin  is 
the  principle  in  hides  that  is  acted  upon  during  the  process  of  tan- 
ning to  make  leather.  Leather  is  not  acted  upon  by  enzymes,  or,  at 
most,  but  sparingly.  Then,  why  not  tan  the  plate  at  the  point  of 
attack  ?  This  was  attempted,  and  a  favorable  result  followed  the 
use  of  a  strong  solution  of  chrome  alum,  producing  a  sort  of  chrome 
tannage.  The  procedure  was  simple  and  rapid,  and  consisted  in 
removing  the  fluid  portion  from  the  gelatin  with  a  pipette  and 
replacing  it  with  the  chrome  alum  solution.  The  effect  was  instanta- 
neous. The  action  of  the  enzyme  was  arrested,  and,  in  addition, 
the  reduced  chromium  made  a  green  area  around  the  colony  just  as 
far  as  the  tanning  process  had  penetrated,  and  thus  served  as  a  true 
indicator  of  the  amount  of  the  plate  destroyed.  At  the  same  time, 
being  transparent,  it  permitted  the  counting  of  any  colonies  pre- 
viously developed  within  its  zone  of  encroachment. 
Enzymes  seem  to  be  more  or  less  misunderstood  ;  at  least  there 
are  statements  from  authoritative  sources  concerning  them  that  do 
not  agree  entirely.  For  example,  on  page  650,  Sadtler  and  Trimble's 
Pharmaceutical  and  Medical  Chemistry,  will  be  found  the  statement 
that  the  activity  of  all  enzymes  is  destroyed  by  boiling  with  water, 
and  not  destroyed  by  antiseptics.  From  other  sources  we  have 
been  taught  that  antiseptics  do  destroy  enzymes.  The  light  of 
recent  investigation  inclines  to  the  belief  that  these  horizontal  state- 
ments cannot  be  wholly  sustained. 
Drs.  Abbott  and  Gildersleeve,  University  of  Pennsylvania,  have 
definitely  shown  that  proteolytic  ferments  produced  during  the 
growth  of  such  bacteria  as  Bacillus  pyocyaneus,  or  Bacillus  subtilis, 
etc.,  are  not  destroyed  by  boiling  water  and  are  not  prevented  from 
exercising  their  digestive  function  by  antiseptics — at  least,  by  such 
an  antiseptic  as  carbolic  acid.  They  found  that  these  enzymes 
resisted  the  temperature  of  boiling  water  when  exposed  to  it  from 
fifteen  to  thirty  minutes,  and  afterwards  attacked  and  completely 
digested  a  medium  consisting  of 
Gelatin   8"  c.c. 
Phenol    -25  " 
Water  ioo*  " 
and  did  this  with  but  slightly  diminished  vigor. 
The  science  of  water  purification  is  a  many-sided  one,  and  each 
side  has  its  peculiar  difficulties.    This  seems  especially  true  of  the 
