648 
]\IE.  J.  LISTEE  OJs"  THE  EAELT  STAGES  OE  IXELAZ^rVIATIOH. 
each  “rouleau”  adhering  to  other  rouleaux,  a network  is  produced  with  intervals  of 
colourless  liquor  sanguinis.  Rapid  movement  of  the  blood  prevents  this  occuiTence,  hut 
it  commences  as  soon  as  the  corpuscles  approach  to  a state  of  quiescence,  and  I have 
seen  short  rouleaux  already  present  in  a drop  drawn  from  my  own  finger  within  ten 
seconds  of  its  emission.  In  this  respect  the  aggregation  of  the  red  corpuscles  differs 
from  the  coagulation  of  the  fibrine,  which  does  not  begin  till  some  minutes  after  with- 
drawal from  the  vessels.  There  is,  in  fact,  no  connexion  whatever  between  the  two 
processes,  as  is  clear  from  the  circumstance  that  if  a drop  of  blood  is  stm-ed  with  a 
needle  while  coagulation  is  taking  place,  so  as  to  remove  the  whole  of  the  fibrine,  the 
corpuscles,  which  have  been  separated  from  one  another  by  the  agitation  to  which  they 
have  been  subjected,  aggregate  again  in  the  serum  in  the  same  manner  as  they  did  at 
first  in  the  liquor  sanguinis.  The  beautifully  regular  form  of  the  long  masses  of 
corpuscles  has  suggested  to  some  persons  the  idea  of  the  operation  of  some  pecuhar 
vital  attraction  in  their  formation,  while  by  others  the  aggregation  has  been  supposed 
due  to  merely  physical  causes,  but  has  never,  I think,  received  a complete  explanation. 
For  my  own  part,  I am  satisfied  that  the  rouleaux  are  simply  the  result  of  the  biconcave 
form  of  the  red  discs,  together  with  a certain,  though  not  very  great  degree  of  adhesive- 
ness, which  retains  them  pretty  firmly  attached  together  when  in  the  position  most 
favourable  for  its  operation,  namely,  when  the  margins  of  them  concave  sin-faces  are 
applied  accurately  together,  but  allows  them  to  shp  upon  one  another  when  hi  any 
other  position.  There  is  never  to  be  seen  anything  indicating  the  existence  of  an 
attractive  force  drawing  the  corpuscles  towards  each  other : they  merely  stick  together 
when  brought  into  contact  by  accidental  causes.  Their  adhesiveness  does  not  affect 
themselves  alone,  but  other  substances  also,  as  may  be  seen  when  blood  is  m motion 
in  an  extremely  thin  film  between  two  plates  of  glass,  when  they  may  be  ohserveil 
sticking  for  a longer  or  shorter  time  to  one  of  the  surfaces  of  the  glass,  each  one 
dragging  behind  it  a short  tail-like  process ; and  as  the  movement  of  the  blood  dimi- 
nishes so  as  to  permit  the  formation  of  rouleaux,  the  latter  may  be  not 
unfrequently  seen  adhering  in  the  same  way  by  one  of  then  terminal 
corpuscles,  as  represented  in  the- accompanying  diagram. 
That  the  cylindrical  character  of  the  aggregated  masses  is  an  accidental  result  of  the 
shape  of  the  blood-discs,  is  evident  from  the  fact,  that  ui 
the  frog,  although  the  same  tendency  to  agglutination  of 
the  corpuscles  exists  as  in  Mammalia,  yet,  as  their  bi- 
convex form  renders  it  mechanically  impossible  for  them 
to  be  applied  to  one  another  throughout  then  entire  cir- 
cumference, they  become  arranged  in  groups  of  an  irre- 
gular form,  as  is  shown  in  the  annexed  sketch  of  blood 
contained  in  a small  vein  of  the  frog’s  web. 
Again,  different  specimens  of  mammalian  blood  difter  very  much  in  the  amount  of 
adhesiveness  of  their  corpuscles  ; and  when  this  property  exists  beyond  a certain  degree. 
