﻿320 
  Dr. 
  M. 
  Foster 
  and 
  Mr. 
  A. 
  G. 
  Dew-Smith 
  on 
  the 
  [Mar. 
  18, 
  

  

  removing 
  the 
  heart 
  from 
  the 
  body, 
  it 
  is 
  of 
  importance, 
  in 
  order 
  to 
  secure 
  

   a 
  good 
  rhythmic 
  beat, 
  that 
  the 
  incision 
  should 
  be 
  carried 
  through 
  the 
  

   aorta, 
  and 
  not 
  invade 
  the 
  contractile 
  tissue 
  of 
  the 
  ventricle 
  itself. 
  

  

  While 
  the 
  auricle 
  is 
  a 
  sac, 
  with 
  quite 
  thin 
  and 
  smooth 
  walls, 
  the 
  

   bundles 
  of 
  fibres 
  in 
  the 
  ventricular 
  walls 
  bulge 
  out 
  largely 
  into 
  the 
  cavity, 
  

   and 
  are 
  so 
  arranged 
  that 
  the 
  ventricle 
  has 
  the 
  same 
  spongy 
  structure 
  as 
  

   that 
  of 
  the 
  frog 
  and 
  many 
  other 
  animals. 
  

  

  Neither 
  in 
  the 
  auricular 
  nor 
  ventricular 
  wall 
  can 
  the 
  presence 
  of 
  any 
  

   nerve-cells, 
  or 
  collection 
  of 
  nerve-cells 
  in 
  the 
  form 
  of 
  ganglia, 
  be 
  detected, 
  

   whether 
  in 
  fresh 
  specimens 
  or 
  in 
  those 
  treated 
  with 
  various 
  reagents. 
  

   The 
  interlacing 
  intricately 
  arranged 
  bundles 
  of 
  fibres 
  are 
  composed 
  of 
  a 
  

   granular 
  protoplasmic-looking 
  tissue, 
  quite 
  unlike 
  the 
  ordinary 
  muscular 
  

   tissue 
  of 
  the 
  body, 
  and 
  in 
  many 
  ways 
  resembling 
  the 
  cardiac 
  tissue 
  of 
  

   vertebrates. 
  

  

  The 
  walls 
  are 
  thickly 
  studded 
  with 
  nuclei, 
  some 
  of 
  which 
  possibly 
  

   belong 
  to 
  an 
  external 
  tesselated 
  epithelium. 
  Other 
  nuclei 
  are 
  un- 
  

   doubtedly 
  the 
  proper 
  nuclei 
  of 
  the 
  contractile 
  elements, 
  and 
  the 
  re- 
  

   mainder 
  seem 
  to 
  be 
  of 
  the 
  nature 
  of 
  connective 
  tissue. 
  

  

  Of 
  none 
  of 
  them 
  can 
  it 
  safely 
  be 
  said 
  that 
  they 
  are 
  the 
  nuclei 
  of 
  nerve- 
  

   cells. 
  Molluscan 
  nerve-fibres 
  might 
  undoubtedly, 
  unlike 
  vertebrate 
  

   medullated 
  nerve-fibres, 
  easily 
  escape 
  detection 
  ; 
  but 
  Mr. 
  A. 
  S. 
  Lea, 
  of 
  

   Trinity 
  College, 
  carefully 
  examined 
  for 
  us 
  the 
  whole 
  of 
  both 
  the 
  auricle 
  

   and 
  ventricle 
  without 
  discovering 
  any 
  distinct 
  nervous 
  structures. 
  He 
  

   also 
  went 
  systematically 
  over 
  the 
  margins 
  of 
  both 
  the 
  aortic 
  and 
  pulmo- 
  

   nary 
  orifices, 
  but 
  could 
  find 
  no 
  nerves 
  running 
  into 
  or 
  out 
  of 
  the 
  heart. 
  

   In 
  no 
  other 
  way 
  could 
  nerves 
  become 
  connected 
  with 
  the 
  heart. 
  And, 
  

   opposed 
  as 
  it 
  may 
  seem 
  to 
  general 
  experience, 
  and 
  still 
  more 
  to 
  recog- 
  

   nized 
  opinions, 
  we 
  are 
  led 
  to 
  the 
  conclusion 
  that 
  the 
  heart 
  of 
  the 
  snail 
  

   has 
  no 
  nervous 
  connexion 
  with 
  the 
  rest 
  of 
  the 
  body 
  ; 
  nay, 
  more, 
  that 
  it 
  

   has 
  within 
  itself 
  no 
  distinctly 
  specialized 
  nervous 
  mechanism, 
  but 
  that 
  

   its 
  contractile 
  elements 
  are 
  composed 
  of 
  protoplasm, 
  arranged, 
  it 
  is 
  true, 
  

   more 
  or 
  less 
  in 
  fibres, 
  yet 
  otherwise 
  but 
  slightly 
  advanced 
  in 
  dif- 
  

   ferentiation. 
  

  

  The 
  Effects 
  of 
  single 
  Induction-shocks. 
  

  

  A 
  single 
  induction-shock 
  sent 
  through 
  the 
  ventricle 
  of 
  the 
  snail's 
  heart 
  

   produces 
  different 
  results, 
  according 
  to 
  the 
  strength 
  of 
  the 
  current 
  em- 
  

   ployed. 
  We 
  have 
  generally 
  used 
  the 
  closing 
  shock 
  alone, 
  or 
  the 
  opening 
  

   shock 
  alone, 
  stopping 
  the 
  other 
  shock 
  in 
  the 
  usual 
  way. 
  Except 
  that 
  

   the 
  opening 
  shock 
  acts, 
  of 
  course, 
  as 
  a 
  stronger 
  stimulus 
  than 
  the 
  closing 
  

   shock, 
  we 
  have 
  not 
  observed 
  any 
  marked 
  difference 
  between 
  their 
  effects. 
  

  

  When 
  the 
  shock 
  is 
  of 
  a 
  certain 
  intensity 
  (as, 
  for 
  instance, 
  when 
  a 
  

   single 
  Darnell's 
  cell 
  is 
  used 
  with 
  the 
  secondary 
  coil 
  of 
  a 
  Du 
  Bois 
  Eeymond's 
  

   induction- 
  machine 
  drawn 
  out 
  to 
  5 
  or 
  10), 
  its 
  application 
  is 
  immediately 
  

   followed 
  by 
  a 
  contraction. 
  This 
  contraction 
  has 
  all 
  the 
  characters 
  of 
  a 
  

   normal 
  beat, 
  except 
  perhaps 
  that 
  it 
  is 
  rather 
  more 
  sudden 
  and 
  of 
  shorter 
  

  

  