n8  Creatinin  and  Creatin  in  the  Blood.  {^bmSy,1*^™' 
cate  0.5  Mg.  as  the  upper  limit  of  normality ;  and  they  have  reported 
many  specimens  of  normal  blood  to  contain  as  little  as  0.1  Mg. 
The  problem  of  establishing  definitely  a  standard  of  composition  is 
further  complicated  by  the  fact  that  creatinin  has  been  demonstrated 
to  occur  in  the  corpuscles  as  well  as  in  the  plasma.  Obviously  only 
the  plasma  component  can  be  concerned  directly  in  the  passage  of 
creatinin  in  or  out  of  the  circulation.  As  a  recent  writer  has  ex- 
pressed it,  the  accumulation  of  creatinin  in  the  blood  has  shown 
itself  to  be  a  useful  index  of  renal  insufficiency ;  but  we  are  as  yet 
unaware  whether  the  excess  present  in  the  circulation  of  a  nephritic 
permeates  all  the  elements  of  the  blood,  or  accumulates  in  the  plasma 
alone.  If  the  latter  alternative  should  prove  to  be  correct,  the 
variations  of  the  plasma  creatinin  in  kidney  disease  would  be  even 
more  striking  than  those  of  the  whole  blood  creatinin,  and  would 
form  a  still  more  delicate  index  of  the  organ's  capacity  to  excrete. 
A  separate  study  of  plasma  and  whole  blood  creatinin  and  creatin 
in  different  pathologic  conditions  might  even  reveal  significant  varia- 
tions in  the  permeability  of  the  corpuscles  for  these  substances. 
Thanks  to  the  researches  of  Wilson  and  Plass,  of  the  Johns 
Hopkins  Medical  School,  and  more  recently  of  Hunter  and  Camp- 
bell at  the  University  of  Toronto,  it  seems  conclusive  now  that  in 
general  the  creatinin  of  normal  human  blood  is  distributed  among 
its  different  elements  at  a  practically  uniform  concentration.  It  is 
not  confined  more  particularly  to  either  plasma  or  corpuscles.  The 
figures  ascertained  for  the  plasma  indicate,  therefore,  also  the  true 
creatinin  content  of  whole  blood.  According  to  Hunter  and  Camp- 
bell, the  creatinin  content  of  normal  human  blood  plasma  ranges 
under  different  conditions  from  0.7  to  1.3  Mg.  per  hundred  Cc,  the 
average  for  sixty  specimens  examined  being  1  Mg.  This  is  in  sub- 
stantial agreement  with  the  figures  of  all  the  previous  workers  ex- 
cept Gettler,  whose  divergent  results  were  reported  above. 
With  respect  to  the  content  of  creatin  in  the  blood,  the  condi- 
tions are  apparently  unlike  the  equal  distribution  of  creatinin.  Hun- 
ter and  Campbell  believe  that  the  creatin  is  chiefly  concentrated  in 
the  corpuscles.  With  the  method  used,  exact  determinations  were 
unattainable ;  but  it  is  roughly  estimated  that  the  average  creatin 
content  of  the  corpuscles  lies  between  6  and  9  Mg.  per  hundred  Cc, 
while  that  of  the  plasma  is  not  more  than  from  0.4  to  0.6.  The 
blood  as  a  whole  contains  apparently  an  average  of  about  3  Mg.  per 
hundred  Cc.    There  seems  to  be  more  in  the  blood  of  females  than 
