UREA  RELATIVE  TO  ANIMAL  PHYSIOLOGY. 
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UREA  IN  ITS  RELATIONS  TO  THE  GENERAL  PHENOMENA  OF 
ANIMAL  PHYSIOLOGY. 
By  Thomas  Bischoff. 
There  is  no  longer  any  doubt  that  accurate  knowledge  of  the 
phenomena  of  animal  organism  can  only  be  acquired  by  the  aid 
of  a  more  intimate  acquaintance  with  the  unceasing  chemical 
metamorphoses  which  take  place  in  them.  These  changesjnust 
be  understood,  not  only  qualitatively  but  quantitatively,  before 
our  views  on  this  subject  can  possess  any  scientific  precision. 
Towards  the  attainment  of  this  object  much  has  already  been 
achieved,  but  indefinitely  more  remains  to  be  done.  This  is  par- 
ticularly the  case  with  regard  to  the  metamorphoses  of  the  nitro- 
genous constituents  of  the  organism  which  are  justly  considered 
to  be  of  such  predominant  importance  in  its  actual  activity.  The 
history  of  the  nitrogenous  elements  of  food  is  at  the  present  time 
incomparably  more  extended  and  minute  than  formerly.  So 
likewise  the  study  of  the  nitrogenous  excretions,  particularly 
urea,  has  been  abundantly  and  productively  cultivated.  No 
doubt  is  entertained  that  it  is  derived  from  the  nitrogenous  ele- 
ments of  food,  but  with  regard  to  the  quantitative  and  even 
qualitative  relations  which  obtain  between  them  there  is  the 
greatest  uncertainty  and  diversity  of  opinion. 
While  some  regard  urea  as  the  ultimate  product  of  a  series  of 
metamorphoses  of  the  nitrogenous  elements  of  food  which  can 
be  developed  only  in  the  living  organism  and  by  the  action  of 
the  organs,  others  entertain  the  opinion  that  the  albumen  of  the 
blood  is  converted  directly  into  urea,  even  in  the  blood. 
According  .to  the  former  view,  urea,  independently  of  some 
other  less  important  nitrogenous  excretions,  might  be  regarded 
as  a  quantitative  measure  of  metamorphoses  in  the  nitrogenous 
organs,  a  circumstance  which  would  be  of  incalculable  value  with 
reference  to  the  functions  and  agency  of  these  organs.  Such  a 
proceeding  is,  however,  inconsistent  with  the  latter  view,  which 
represents  the  quantity  of  urea  as  dependent  upon  the  accidental 
quantity  of  albumen  in  the  blood. 
An  unprejudiced  consideration  of  the  researches  which  have 
hitherto  been  instituted  for  the  purpose  of  deciding  these  ques- 
tions, will  at  once  show  that  they  are  altogether  unsatisfactory. 
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