On  the  Power  of  Soils  to  absorb  Manure. 
367 
that  plants  have  actually  the  power  of  feeding:  on  these  primary 
compounds — a view  which  it  is  almost  needless  to  say  has.  been 
all  but  abandoned  by  chemists  and  vegetable  physiologists  of  the 
present  day. 
An  experiment  now  to  be  described  is  rather  in  favour  of  the 
belief  that  clay  actually  prevents  the  putrefactive  process. 
Etj yeriment  95. — Fresh  human  urine  was  filtered  through  white  clay, 
mixed  with  its  own  weight  of  sand.  The  first  portion  came  through  colour- 
less; by  and  by,  however,  the  urine  itself  passed  through  apparently  un- 
changed. Several  ounces  were  collected,  and  by  accident  remained  on  the 
table  beside  a quantity  of  the  same  urine  which  had  not  been  so  filtered. 
At  the  end  of  several  days  it  was  observed  that  the  filtered  urine  was  quite 
sweet,  whilst  the  other  had  passed  into  a state  of  putridity  ; and  for  more 
than  a month,  during  which  it  was  kept,  this  filtered  quantity  remained  in 
the  state,  having  the  smell  of  fresh  mine  without  the  smallest  putridity: 
the  clay  in  fact  had  destroyed  its  power  of  fermentation. 
It  is  believed  that  the  spontaneous  putrefaction  of  urine  is  due 
to  the  presence  of  portions  of  mucus  from  the  bladder,,  and  the 
idea  will  suggest  itself  that  filtration  by  removing  this  mucus  de- 
stroys the  susceptibility  to  spontaneous  change ; but  I have  found 
that  filtration  through  the  finest  paper  does  not  prevent  urine 
from  fermenting  ; and  further,  that  by  merely  stirring  up  clay 
with  urine — the  latter  being  greatly  in  excess — allowing  the 
liquid  to  clear  itself,  and  pouring  it  off,  further  change  is  altoge- 
ther prevented.  It  is  quite  likely  that  the  clay  combines  with 
the  organic  bodies  acting  as  ferments,  and  thus  removes  them  from 
the  solution  ; but  however  it  may  be  explained,  of  the  fact  there 
can  be  no  dispute. 
The  result  in  the  first 'experiment,  where  urine  and  clay  were 
digested  together,  is  susceptible,'  as  before  said,  of  two  explanations 
— 1st.  That  no  putrefaction  takes  place  ; or.  2nd.  That  the  pro- 
ducts of  putrefaction ' are  absorbed,  and  consequently  do  not 
become  evident  to  the  geqses.  We  have  seen  that  clay  destroys 
the  smell  of  putrid  urine ; -consequently,-  so  fast  as  it  became 
putrid  the  evidence  of  putrefaction  by  smell  would  be  destroyed. 
In  this  way  we  may  suppose  the  whole  of  the  urea  and  other 
animal  matters  to  pass  into  secondary  and  even  final  or  ultimate 
products  of  decomposition  without  the  smallest  external  sign  that 
such  change  had  occurred.  But  this  conclusion  is  irreconcilable 
with  the  fact  that  clay,  when  used  in  small  quantity,  although  it 
removes  only  a part  of  the  animal  matters  of  urine,  destroys  the 
tendency  to  spontaneous  putrefaction  in  that  which  is  left.  The 
inference  from  these  united  observations  would  be,  that  urine  and 
other  animal  liquids,  when  mixed  with  the  soil,  do  not  undergo 
the  ordinary  decomposition. 
No  decided  opinion,  however,  should  be  formed  on  so  important 
a subject  upon  imperfect  data;  and  for  the  present  we  must  be 
content  to  believe  simply,  that  the  phenomena  of  fermentation  and 
