﻿dr 
  davy's 
  observations 
  on 
  the 
  charr. 
  329 
  

  

  As 
  a 
  solution 
  of 
  common 
  salt 
  has 
  the 
  property 
  not 
  only 
  of 
  keeping 
  liquid 
  the 
  

   fluid 
  of 
  the 
  yolk, 
  but 
  also 
  of 
  dissolving 
  its 
  coagulum, 
  it 
  seems 
  well 
  adapted 
  as 
  a 
  

   medium 
  for 
  the 
  purpose 
  of 
  examining 
  the 
  foetal 
  structure. 
  Using 
  it 
  thus, 
  I 
  found 
  

   that 
  an 
  ovum 
  in 
  which 
  the 
  embryo 
  was 
  active 
  on 
  the 
  42d 
  day, 
  immersed 
  in 
  a 
  

   solution 
  of 
  salt 
  of 
  the 
  specific 
  gravity 
  1033, 
  kept 
  therein 
  about 
  half 
  an 
  hour, 
  

   retained 
  its 
  vitality 
  ; 
  and 
  that, 
  excluded 
  by 
  an 
  opening 
  artificially 
  made 
  in 
  the 
  

   shell, 
  the 
  young 
  fish 
  remaining 
  in 
  the 
  solution, 
  continued 
  active 
  for 
  another 
  half 
  

   hour. 
  This 
  result 
  led 
  me 
  to 
  try 
  the 
  effect 
  of 
  keeping 
  the 
  ova 
  in 
  solutions 
  of 
  com- 
  

   mon 
  salt, 
  and 
  also 
  the 
  young 
  fish, 
  to 
  ascertain 
  whether 
  the 
  former 
  would 
  be 
  

   hatched, 
  and 
  what 
  would 
  be 
  the 
  effects 
  on 
  the 
  latter. 
  One 
  trial 
  was 
  made 
  with 
  

   the 
  ova, 
  using 
  salt 
  water 
  of 
  the 
  specific 
  gravity 
  mentioned, 
  1033 
  ; 
  another 
  with 
  

   water 
  just 
  perceptibly 
  impregnated 
  with 
  salt, 
  confined 
  in 
  glass 
  bottles 
  and 
  kept 
  

   in 
  the 
  room 
  of 
  the 
  average 
  temperature 
  of 
  about 
  55°. 
  In 
  the 
  stronger 
  solution, 
  

   the 
  ova 
  remained 
  transparent, 
  but 
  no 
  marks 
  of 
  development 
  appeared. 
  In 
  the 
  

   weaker 
  solution, 
  on 
  the 
  26th 
  of 
  November, 
  — 
  the 
  trial 
  was 
  begun 
  on 
  the 
  4th, 
  — 
  

   black 
  specks 
  denoting 
  eyes, 
  in 
  the 
  act 
  of 
  forming, 
  were 
  observable 
  in 
  four 
  ova, 
  

   and 
  vessels 
  carrying 
  red 
  blood 
  in 
  the 
  vitelline 
  membrane. 
  In 
  this 
  stage, 
  further 
  

   progress 
  was 
  arrested 
  by 
  death. 
  The 
  first 
  experiment 
  on 
  a 
  young 
  fish 
  was 
  made 
  

   on 
  one 
  that 
  had 
  been 
  hatched 
  about 
  22 
  days. 
  Put 
  into 
  sea-water, 
  diluted 
  with 
  

   spring-water 
  so 
  as 
  to 
  be 
  of 
  specific 
  gravity 
  1020, 
  it 
  was 
  found 
  dead 
  three 
  hours 
  

   after 
  ; 
  it 
  was 
  contracted 
  in 
  length 
  from 
  -68 
  to 
  *46 
  of 
  an 
  inch. 
  The 
  next 
  was 
  on 
  

   a 
  young 
  charr 
  of 
  the 
  same 
  age 
  : 
  this, 
  immersed 
  in 
  a 
  solution 
  of 
  the 
  specific 
  gravity 
  

   10036, 
  after 
  24 
  hours, 
  seemed 
  as 
  active 
  as 
  before. 
  More 
  salt 
  was 
  then 
  added 
  so 
  

   as 
  to 
  increase 
  the 
  specific 
  gravity 
  to 
  10068, 
  but 
  still 
  without 
  marked 
  effect. 
  

   After 
  other 
  24 
  hours 
  the 
  specific 
  gravity, 
  by 
  another 
  addition 
  of 
  salt, 
  was 
  raised 
  

   to 
  10098 
  ; 
  now 
  the 
  fish 
  became 
  more 
  restless, 
  as 
  if 
  seeking 
  to 
  escape. 
  After 
  the 
  

   same 
  interval 
  a 
  fresh 
  portion 
  of 
  salt 
  was 
  introduced, 
  raising 
  the 
  specific 
  gravity 
  

   to 
  10153 
  : 
  the 
  effect 
  now 
  was 
  strongly 
  marked 
  ; 
  in 
  about 
  six 
  hours 
  the 
  fish 
  was 
  

   found 
  motionless, 
  except 
  the 
  lower 
  jaw, 
  which, 
  under 
  the 
  microscope, 
  exhibited 
  a 
  

   tremulous 
  movement, 
  and 
  except 
  the 
  heart, 
  which 
  still 
  acted 
  pretty 
  vigorously, 
  

   and 
  which 
  continued 
  to 
  act, 
  but 
  with 
  decreasing 
  force, 
  for 
  about 
  20 
  hours, 
  reckon- 
  

   ing 
  from 
  the 
  time 
  that 
  the 
  fish 
  first 
  appeared 
  motionless 
  and 
  moribund. 
  

  

  The 
  next 
  trials 
  I 
  shall 
  mention 
  were 
  made 
  with 
  the 
  intent 
  to 
  endeavour 
  to 
  

   ascertain 
  how 
  long 
  } 
  r 
  oung 
  charr 
  might 
  be 
  kept 
  alive 
  in 
  the 
  same 
  portion 
  of 
  water, 
  

   and 
  that 
  a 
  small 
  quantity, 
  such 
  as 
  might 
  be 
  used 
  in 
  conveying 
  the 
  fish 
  from 
  place 
  

   to 
  place 
  at 
  an 
  early 
  age, 
  when, 
  before 
  the 
  yolk 
  is 
  exhausted, 
  it 
  stands 
  in 
  no 
  need 
  of 
  

   a 
  supply 
  of 
  food 
  from 
  without. 
  Two 
  experiments 
  were 
  made, 
  one 
  with 
  a 
  portion 
  

   of 
  pure 
  oxygen 
  over 
  the 
  water, 
  the 
  other 
  with 
  common 
  air. 
  The 
  volume 
  of 
  water 
  

   and 
  air 
  in 
  each 
  instance 
  was 
  nearly 
  equal 
  — 
  about 
  four 
  ounce 
  measures, 
  — 
  the 
  

   capacity 
  of 
  the 
  containing 
  bottle 
  being 
  about 
  eight 
  ounces. 
  The 
  bottles, 
  after 
  

   the 
  introduction 
  of 
  the 
  young 
  fish, 
  were 
  closed 
  with 
  a 
  glass 
  stopper 
  and 
  inverted 
  

   vol. 
  xx. 
  part 
  in. 
  4 
  u 
  

  

  