694 
ME.  J.  LISTEE  ON  THE  EAELT  STAGES  OE  ENFLAMMATION. 
parts  of  the  field.  For  the  sake  of  confirmation  I again  operated  in  a similar  manner 
upon  another  specimen,  on  which  I performed  no  less  than  five  successive  experiments 
with  similar  results  in  all.  In  the  first  three  of  these  trials  I had  the  very  same  cilia 
under  observation,  and  saw  them  time  after  time  become  first  increased  in  action  and 
then  arrested  under  the  influence  of  the  cautery,  and  gradually  recover  after  its  removal. 
In  some  instances  the  times  of  cessation  and  of  recovery  were  noted  as  follows : — In  the 
first  the  cilia  were  arrested  in  two  seconds  after  the  application  of  the  hot  iron,  but  the 
exact  time  of  recovery  was  not  observed ; in  the  second,  cessation  of  movement  was  pro- 
duced in  two  seconds,  and  return  began  in  fifteen  seconds ; in  the  third,  cessation  was  in 
fifteen  seconds,  and  recovery  also  in  fifteen  seconds ; in  the  fourth,  the  times  were  not 
noted ; in  the  fifth,  movement  ceased  in  about  two  seconds  and  returned  in  twenty.  The 
experiments  were  performed  within  about  five  minutes  of  each  other,  or  sometimes  less. 
It  is  also  to  be  remarked,  that  there  were  some  slight  differences  in  the  degree  of  heat 
of  the  cautery  and  its  vicinity  to  the  object. 
These  experiments  are  as  instructive  as  they  are  simple  and  easy  of  performance. 
They  show  conclusively  that  a component  tissue  of  the  animal  frame  may,  indepen- 
dently of  the  nervous  system,  have  its  actions  either  excited  or  paralysed  by  the  direct 
operation  of  an  irritant  upon  it,  and  that  it  may  possess  an  equally  independent  power 
of  recovery.  Also  in  the  accelerated  movements  of  the  cilia  elicited  by  very  gentle 
heat,  as  compared  with  the  cessation  of  their  vibrations  under  a higher  temperature,  we 
have  a striking  confirmation  of  the  view  which  I had  taken  of  the  relaxation  of  the 
arteries  and  hollow  viscera  in  consequence  of  nervous  irritation*.  For  the  law  which 
we  thus  see  regulating  the  effects  of  heat  upon  the  epithehum-cells  is  precisely  that 
which  I had  inferred  must  govern  the  action  of  afferent  nerves  upon  neiwe-cells ; this 
law  being,  that  an  agency  which,  when  operating  mildly,  stimulates  a tissue  to  increased 
activity,  may,  when  more  energetic,  temporarily  arrest  its  functions.  'SATiether  or  not 
the  converse  always  holds,  viz.  that  any  agent  which  is  capable  of  suspending  the  func- 
tional activity  of  a tissue  may  also  excite  it  if  applied  with  sufiicient  gentleness,  or,  in 
other  words,  whether  irritants  are  in  all  cases  also  stimulants,  seems  very  doubtful. 
As  regards  the  nerves,  such  does  appear  to  be  the  case ; for  while  many,  and  probably 
all  influences  which  induce  inflammatory  congestion  cause  temporary  paralysis  of  sensa- 
tion in  parts  on  which  they  act  severely  enough,  they  all  stimulate  the  afferent  nerves 
in  the  first  instance,  as  is  shown  by  the  reflex  changes  in  the  calibre  of  the  arteries  which 
occur  round  about  any  irritated  spot.  The  nervous  centres,  too,  present  an  illustration 
of  the  same  principle,  not  only  in  the  effects  produced  upon  them  by  the  nerves,  as  lately 
alluded  to,  but  also  in  the  excitement  well  known  to  be  occasioned  by  small  doses  of 
many  sedative  narcotics,  such  as  alcohol,  opium,  and  chloroform,  which  may  be  regarded 
as  special  irritants  of  the  nervous  centres.  In  the  case  of  the  cilia,  I have  not  observed 
primary  increase  of  movement  to  be  induced  by  any  agent  besides  heat ; but  I am  not 
prepared  to  say  that  it  might  not  by  careful  management  be  made  to  occur-  with  some 
other  irritants. 
* Vide  antea,  p.  666. 
