﻿Circulation 
  of 
  the 
  Blood. 
  

  

  145 
  

  

  pulse-rate 
  and 
  becoming 
  nil 
  when 
  it 
  is 
  170 
  a 
  minute, 
  which 
  may 
  be 
  fairly- 
  

   conceived 
  to 
  be 
  very 
  near 
  the 
  limit 
  of 
  cardiac 
  rapidity 
  in 
  man. 
  

  

  That 
  this 
  interval 
  (the 
  syspasis) 
  should 
  vary 
  so 
  considerably 
  in 
  length 
  

   with 
  differeut 
  pulse-rates 
  is 
  not 
  easy 
  to 
  explain 
  at 
  first 
  sight 
  ; 
  never- 
  

   theless 
  a 
  careful 
  review 
  of 
  the 
  different 
  processes 
  which 
  are 
  in 
  operation 
  

   in 
  the 
  heart 
  at 
  the 
  time 
  has 
  suggested 
  to 
  me 
  an 
  explanation 
  which 
  seems 
  

   reasonable. 
  It 
  depends 
  on 
  the 
  fact 
  that 
  the 
  extreme 
  shortness 
  of 
  the 
  

   diastole 
  makes 
  any 
  variation 
  in 
  its 
  length 
  have 
  a 
  marked 
  influence 
  on 
  the 
  

   amount 
  of 
  blood 
  which 
  enters 
  the 
  capillaries 
  of 
  the 
  walls 
  of 
  the 
  heart, 
  

   and 
  consequently 
  influences 
  the 
  amount 
  of 
  work 
  which 
  the 
  muscular 
  

   fibres 
  of 
  the 
  ventricle 
  have 
  to 
  perform 
  in 
  emptying 
  their 
  interstitial 
  

   vessels 
  before 
  they 
  can 
  commence 
  contracting 
  on 
  the 
  blood 
  in 
  their 
  con- 
  

   tained 
  cavity. 
  Experiment 
  shows 
  that 
  the 
  rapidity 
  of 
  the 
  pulse 
  does 
  not 
  

   depend 
  on 
  the 
  pressure 
  of 
  the 
  blood 
  in 
  the 
  arterial 
  system* 
  ; 
  conse- 
  

   quently 
  the 
  length 
  of 
  the 
  syspasis 
  is 
  not 
  influenced 
  by 
  the 
  arterial 
  blood- 
  

   pressure, 
  which 
  is 
  the 
  same 
  thing 
  as 
  saying 
  that 
  the 
  force 
  of 
  the 
  cardiac 
  

   contraction 
  varies 
  directly 
  as 
  the 
  blood-pressure 
  ; 
  for 
  then 
  the 
  muscular 
  

   power 
  of 
  the 
  ventricular 
  walls 
  to 
  overcome 
  the 
  intramural 
  distention, 
  

   varying 
  with 
  it, 
  prevents 
  its 
  duration 
  from 
  being 
  modified. 
  

  

  It 
  has 
  been 
  my 
  endeavour 
  to 
  show 
  elsewhere 
  f 
  that 
  the 
  force 
  of 
  the 
  

   heart's 
  contraction 
  is 
  modified 
  by 
  the 
  length 
  of 
  diastole, 
  varying 
  as 
  its 
  

   square 
  root. 
  Such 
  being 
  the 
  case, 
  it 
  is 
  evident 
  that 
  the 
  length 
  of 
  the 
  

   syspasis 
  must 
  vary 
  with 
  that 
  of 
  the 
  diastole, 
  though 
  not 
  to 
  the 
  extent 
  

   that 
  is 
  found 
  to 
  occur. 
  Eut 
  the 
  diastolic 
  period 
  being 
  always 
  so 
  short, 
  

   it 
  is 
  evident 
  that 
  the 
  longer 
  it 
  is, 
  the 
  more 
  thoroughly 
  does 
  the 
  heart- 
  

   tissue 
  get 
  permeated 
  with 
  blood, 
  in 
  a 
  way 
  which 
  can 
  have 
  little 
  or 
  no 
  

   influence 
  on 
  its 
  nutritive 
  power, 
  but 
  a 
  great 
  effect 
  in 
  modifying 
  the 
  length 
  

   of 
  the 
  syspasis 
  in 
  the 
  direction 
  which 
  is 
  found 
  to 
  occur. 
  

  

  Again, 
  referring 
  to 
  the 
  results 
  of 
  the 
  cardio-sphygmograph 
  observations 
  

   published 
  by 
  me 
  in 
  the 
  1 
  Proceedings 
  ' 
  of 
  this 
  Society 
  (vol. 
  xix. 
  p. 
  318), 
  

   that 
  paper 
  contains 
  a 
  Table 
  of 
  the 
  length 
  of 
  the 
  different 
  cardio-arterial 
  

   intervals 
  ; 
  and 
  if 
  from 
  the 
  first 
  cardio-arterial 
  interval, 
  as 
  there 
  defined, 
  

   the 
  length 
  of 
  the 
  syspasis 
  be 
  subtracted 
  at 
  the 
  corresponding 
  rates, 
  it 
  

   will 
  be 
  found 
  that 
  the 
  remainder 
  of 
  the 
  interval 
  is 
  of 
  exactly 
  the 
  same 
  

   length 
  as 
  the 
  second 
  cardio-arterial 
  interval, 
  which, 
  on 
  the 
  assumptions 
  

   made, 
  it 
  could 
  only 
  be, 
  as 
  both 
  the 
  systole 
  and 
  the 
  shock 
  of 
  the 
  closure 
  of 
  

   the 
  aortic 
  valve 
  are 
  propagated 
  along 
  the 
  arteries 
  from 
  the 
  same 
  point 
  

   under 
  similar 
  circumstances. 
  The 
  following 
  Table 
  gives 
  the 
  lengths 
  of 
  

   the 
  first 
  cardio-arterial 
  interval 
  from 
  which 
  that 
  of 
  the 
  syspasis 
  as 
  above 
  

   determined 
  has 
  been 
  subtracted, 
  and 
  by 
  their 
  side 
  the 
  lengths 
  of 
  the 
  

   second 
  cardio-arterial 
  interval, 
  as 
  copied 
  from 
  the 
  Table 
  in 
  the 
  communi- 
  

   cation 
  referred 
  to 
  ; 
  their 
  similarity 
  cannot 
  be 
  the 
  result 
  of 
  simple 
  coincidence, 
  

   as 
  they 
  are 
  derived 
  from 
  independent 
  sets 
  of 
  measurements. 
  

  

  * 
  Journal 
  of 
  Anatomy 
  and 
  Physiology, 
  Nov. 
  1873. 
  

   t 
  Ibid. 
  vol. 
  viii. 
  

  

  