662 
ME.  J.  LISTEE  ON  THE  EAELT  STAGES  OP  rNTLA:SOIATION. 
the  extreme  margin  of  the  mustard,  which  was  slightly  transparent,  were  obserred  to 
be  of  crimson  colom-,  in  consequence  of  their  containing  closely-crammed  corpuscles, 
some  of  which  were  still  moving,  while  others  were  motionless.  On  the  application  of 
a higher  power,  the  continuations  of  these  capillaries  immediately  exterior  to  the  mustard 
showed,  many  of  them,  red  corpuscles  sticking  to  their  walls,  and  more  or  less  obstruct- 
ing the  progress  of  the  blood  through  them. 
In  the  accompanying  sketch  of  the  vessels  at 
one  part,  together  with  those  corpuscles  which 
were  motionless  in  them,  M represents  the  edge 
of  the  mustard,  a a capillary  partly  overlaid  by 
the  mustard  and  crammed  with  stagnant  cor- 
puscles, h a capillary  with  red  discs  adhering 
to  its  internal  surface,  but  still  transmitting 
blood,  while  further  from  the  mustard  all  the 
corpuscles  were  in  motion,  and  consequently 
none  appear  in  the  drawing;  c was  a rouleau 
of  red  corpuscles  projecting  from  a stagnant 
mass  into  the  vein  V,  through  which  the  blood 
was  flowing  rapidly ; yet  the  rouleau,  though  its 
free  end  was  moved  to  and  fro  by  the  current, 
was  prevented  by  the  mutual  adhesiveness  of  its 
corpuscles  from  being  broken  up  or  detached. 
Thus  it  was  evident  that  in  the  capillaries  of 
the  space  covered  by  the  mustard,  the  red  cor- 
puscles had  an  abnormal  tendency  to  adhere 
both  to  the  walls  of  the  vessels  and  to  one  another,  and  were  on  this  account  accumu- 
lating and  sticking  within  them,  while  almost  immediately  outside  the  mustard,  the  blood 
in  the  capillaries  presented  the  same  appearance  as  in  other  parts  of  the  web.  This  effect 
was  independent  of  changes  in  the  calibre  of  the  vessels,  for  any  results  of  alteration  in 
the  size  of  the  artery  under  the  mustard  must  have  been  shared  by  the  surrounding  capil- 
laries, which  also  derived  their  blood  chiefly  from  it ; and  that  the  vessel  was  dilated 
to  the  same  degree  there  as  elsewhere,  was  shown  by  the  fact,  that  its  branches  con- 
tinued throughout  the  experiment  to  transmit  full  streams  of  blood  after  emerging  from 
beneath  the  opaque  mass.  I also  measured  some  capillaries  by  micrometer  before  the 
application  of  the  mustard,  and  again  after  it  had  caused  stagnation  in  them,  and  found 
that  their  dimensions  remained  the  same*. 
* The  increased  pressure  upon  the  blood  in  the  capillaries,  resulting  from  obstruction  to  the  progress  of 
the  corpuscles,  leads  to  the  distension  of  their  elastic  parietes  up  to  a certain  point,  but,  generally  speaking^ 
not  further.  In  the  present  case,  before  the  application  of  the  mustard,  the  web,  irritated  probably  by  the 
vapour  of  the  chloroform,  was  affected  with  a slight  congestive  tendency,  far  short  of  that  which  induces 
stagnation,  but  yet  sufficient  to  give  rise  to  full  distension  of  the  capillaries.  When  the  web  has  been  per- 
fectly healthy  to  begin  with,  I have  seen  a marked  increase  of  calibre  in  the  capillaries  on  the  occurrence  ot 
