5*4 
Perimetric  Dimension  System. 
(  Am.  Jour.  Pharos. 
\      Dec,  1879. 
able  makes  of  that  admirable  instrument,  have  found  that  a  ready  means 
of  verifying  or  correcting  its  index  was  needed.  One  now  in  use,  and  an 
otherwise  faultless  piece  of  mechanism,  being  accurately  measured 
over  the  knife  in  place,  shows  an  excess  of  size  over  that  registered  of 
4  mm.  An  error  like  this  not  recognized  and  provided  against,  in  an  ope- 
ration of  such  delicacy  and  gravity  as  that  of  Otis's  for  internal  urethro- 
tomy—in  which  the  only  hope  uf  success  depends  upon  strict  accuracy 
and  correspondence  of  measurements — may  at  any  moment  be  the 
source  of  serious  mischief,  or  even  of  fatal  results.  Again,  Ellin- 
ger's  dilator  for  the  cervix  uteri  has  a  seemingly  perfect  parallel 
motion,  but  when  measured  by  the  gauge  shows  a  conicity  of 
12  mm.,  which  is  increased  to  2  cm.  or  more  by  pressure  near  the 
points  when  its  sides  are  separated.  Its  failure  to  be  retained  when  in 
use  is  thus  accounted  for.  Or,  an  instance  mentioned  by  a  friend,  a 
steel  sound  which  had  been  looked  upon  as  standard  32  French,  proved 
upon  measurement  to  be  fully  39*5  mm. — an  enormous  error. 
The  gauge  is  a  simple  appliance,  mechanically  similar  to  the  glovers' 
measure,  and  consists  of  a  narrow  flexible  measuring  tape,  graduated  in 
centimeters  and  millimeters  (Fig.  1),  to  which  is  attached  a  hand-piece 
having  a  mortise  for  the  passage  of  the  tape.  A  sliding  loop  is  thus 
formed  (Fig.  2),  within  which  instruments  to  be  measured  are  placed. 
Fig.  2. 
The  two  ends  of  the  gauge  being  drawn  upon  in  opposite  directions 
so  as  snugly  to  embrace  the  enclosed  object,  the  dimensions  of  its  cir- 
cumference if  cylindrical,  or  its  perimeter  if  of  irregular  outline,  are 
indicated  by  arrows  placed  opposite  the  point  of  beginning  of  the  scale. 
The  material  found  best  adapted  for  its  construction  is  an  extra 
heavy  bank  note  or  bond  paper,  the  handle  being  stiffened  with  card- 
board. This  paper  is  very  flexible,  strong  and  durable,  is  readily 
printed  in  fine  but  legible  divisions,  bears  all  ordinary  use  without 
stretching  or  breaking,  and  is  not  perceptibly  affected  by  atmospheric 
changes.  In  practice,  it  answers  well  for  all  purposes,  including  mea- 
surements involving  delicate  cutting  edges. 
