1 2 Mr.  hunter  on  the  Heat,  &c. 
introducing  my  thermometer,  that  it  fell  to  77°;  fa 
that  the  mouth  at  this  part  had  loft  20°  of  heat.  It  gra- 
dually rofe  to  970  again ; but  the  thermometer  in  this  ex- 
periment did  not  fink  fo  low  as  it  would  have  done  in  the 
hand,  if  a piece  of  ice  had  been  held  in  it  fo  long.  Per- 
haps one  reafon  may  be  afligned  : the  furface  under  the 
tongue  being  furrounded  with  warm  parts,  renders  it 
next  to  an  impoflibility  to  cool  it  to  any  greater  degree : 
but  I fufpedt  ftill  another  reafon,  viz.  parts  which  have 
been  in  a habit  of  confiderably  varying  in  this  refpedt, 
as  the  hand,  will  allow  of  greater  latitude,  being  as  it 
were  infenfibly  drawn  into  cold,  nor  fo  fufceptible  of  it, 
as  has  been  already  obferved. 
As  a further  proof,  that  the  more  perfect  animals  are 
capable  of  varying  their  heat,  in  l'ome  degree,  according 
to  the  external  heat  applied,  I fhall  adduce  the  following 
experiments  made  on  the  human  fubjedt. 
The  mouth  being  a part  fo  frequently  in  contadt  with 
the  external  atmofphere  in  the  adtion  of  breathing, 
whatever  is  put  into  it  will  be  fuppofed  to  be  influenced 
by  that  atmofphere;  this  will  always  render  an  experi- 
ment made  in  the  mouth,  relative  to  heat  and  cold,  in 
fome  degree  doubtful.  I imagined  that  the  urethra 
would  anfwer  better,  becaufe  it  is  an  internal  cavity,  and 
can  be  only  influenced  by  heat  and  cold  applied  to  the 
external 
