Of  viewing  the  Current
132
whereas  the  cool  Dews  of  the  Evening  render -
  them  moist  and  pliable;  which  makes
them  chuse  that  time  to  come  abroad.
In  viewing  several  of  the  Objects  here
mentioned,  one  shall  often  observe  the  Blood
passing  through  Vessels  so  minute,  that  the
Globules  of  it  cannot  glide  along  otherwise
than  single,  and  squeezed  into  oblong  Forms:
yet  an  hundred  of  the  red  Globules  of  such
Blood,  if  placed  close  to  one  another  in  a
Row,  would  not  equal  the  Length  of  the
Diameter  of  a  large  Grain  of  Sand;  and
consequently  a  Million  of  them  exceeds  not
a  Grain  of  Sand  in  Bigness  *.
The  Effects  of  Heat  and  Cold  upon  the
Blood  are  well  worth  taking  notice  of:  for
as  Heat  relaxes  the  Vessels,  the  Blood  finds
more  Room  to  move  in,  its  Globules  float  at
greater  Distances,  and  it  circulates  more
freely:  whereas  Cold  so  contracts  the  Vessels, -
  that  the  Globules  are  comprest  together, ¬
  and  the  Blood  is  impeded,  and  in  some
Degree  coagulated  in  the  minute  Capillary
Veins  and  Arteries  of  the  extream  Parts;  as
is  evident  from  the  Swelling  and  Blackness
of  the  Hands  and  Feet  when  exposed  to
severe  Cold.
*  LEEUWEN.  Arc.  Nat.  Tom.  I.  Par.  I.  p.  35
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