5^2  Perimetric  Dimension  System.  {AmbJe0cU,ri87h9arm* 
every  three  of  the  French  sizes — a  somewhat  questionable  improve- 
ment, though  the  only  merit  claimed  for  it  ;  and  in  doing  this  a  new 
and  arbitrary  series  of  numbers  is  introduced — a  serious  disadvantage. 
Thus,  while  No.  I  is  I  mm.  in  diameter,  No.  2  is  15  mm.,  No.  3  is 
2  mm.,  and  so  on  with  a  widening  disparity  till  No.  20  is  reached, 
which  measures  10*5  mm.  by  the  same  method. 
It  will  readily  be  conceded  that  the  demand  among  those  engaged  in 
general  scientific  work  for  unity  of  standard  in  measures  of  length, 
capacity  and  weight,  which  has  resulted  in  the  wide-spread  adoption  of 
the  metric  system,  has  a  practical  basis.  Nor  will  it  be  questioned  that 
the  various  branches  of  the  science  of  medicine  have  need  of  the  im- 
proved methods  and  means  of  observation  and  experiment  which  have 
become  common  to  allied  sciences.  In  the  sub-departments  of 
urethral,  gynaecic  and  rectal  surgery  especially,  there  is  urgent  need 
for  the  establishment  of  a  common  standard  of  measurement  and  record 
of  the  dimensions  of  the  instruments  employed  ;  and — no  less  import- 
ant— by  means  of  these  of  the  caliore  of  the  passages  to  which  they 
relate. 
A  general  system  suited  to  this  wide  range  of  applications,  is  practi- 
cable, and  an  undoubted  necessity — a  system  combining  the  requisites 
of  simplicity,  definiteness  and  convenience  of  use,  together  with 
universal  scientific  intelligibility.  The  attainment  of  this  end  requires 
simply  the  abandonment  of  all  conventional  numbers,  whether  arbitrary  or 
systematic,  as  indicative  of  size,  and  the  adoption  of  actual  circumferential  or 
perimetric  dimensions,  expressed  in  terms  of  the  metric  unit. 
This  system  is  applicable  to  all  specula  and  dilators,  together  with 
their  related  explorers  and  fixed  cutting  instruments,  for  whatever  part 
designed — the  male  or  female  urethra,  the  rectum,  vagina,  cervix  uteri, 
oesophagus,  Eustachian  tube,  or  the  lachrymal  duct. 
In  designating  sizes  and  recording  data  by  the  Perimetric  Dimen- 
sion System,  millimeters  will  naturally  be  used  for  the  smaller  instru- 
ments and  passages,  while  for  the  larger,  as  rectal  and  vaginal,  centi- 
meters should  be  employed.  The  changed  form  of  expression  will 
then  be,  for  example,  20  mm.  instead  of  No.  20,  French  catheter — a 
gain  in  explicitness  with  no  loss  of  brevity  j  and  in  place  of  Sim's  No. 
I  vaginal  dilator,  as  at  present,  its  equivalent,  10  cm.  ;  or,  8  cm.  as^ 
the  proper  substitute  for  No.  10  of  English  rectal  bougies  ;  or,  again,. 
