﻿96 
  REPOET 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  to 
  the 
  pressure, 
  and 
  cold 
  water 
  takes 
  up 
  more 
  than 
  warm 
  water. 
  The 
  

   station 
  water 
  in 
  winter 
  approaches 
  0'^ 
  C. 
  The 
  sui)ply 
  tanks 
  are 
  some 
  

   18 
  feet 
  above 
  the 
  ground, 
  and 
  the 
  water 
  in 
  the 
  s3^stem 
  of 
  pipes 
  leading 
  

   from 
  them 
  is 
  under 
  corresponding 
  pressure. 
  Accordingly, 
  any 
  air 
  

   accompanying 
  the 
  water 
  in 
  these 
  pipes 
  must 
  constantly 
  tend 
  to 
  pass 
  

   into 
  solution, 
  and 
  as 
  the 
  water 
  when 
  taken 
  up 
  from 
  the 
  basin 
  is 
  approx- 
  

   imately 
  saturated 
  for 
  atmospheric 
  pressure 
  the 
  water 
  in 
  the 
  pipes 
  

   must 
  tend 
  to 
  saturate 
  with 
  air 
  for 
  the 
  increased 
  pressure 
  it 
  sustains, 
  or 
  

   to 
  supersaturate 
  for 
  atmospheric 
  pressure. 
  

  

  In 
  the 
  hatchery 
  and 
  the 
  aquaria 
  the 
  water 
  emerges 
  from 
  the 
  pipes 
  

   into 
  ordinary 
  atmospheric 
  pressure, 
  containing 
  in 
  solution 
  more 
  air 
  

   than 
  it 
  can 
  hold 
  at 
  that 
  pressure. 
  The 
  excess 
  of 
  air 
  instantly 
  begins 
  

   to 
  pass 
  off, 
  or 
  evaporate, 
  the 
  rapidity 
  of 
  the 
  process 
  depending 
  on 
  a 
  

   favorable 
  exposure 
  of 
  the 
  water 
  to 
  the 
  air, 
  and 
  therefore 
  on 
  the 
  con- 
  

   formation 
  of 
  the 
  containing 
  vessel, 
  a 
  very 
  shallow 
  open 
  vessel 
  facili- 
  

   tating 
  the 
  escape 
  of 
  air. 
  The 
  aquaria 
  are 
  not 
  particularly 
  adapted 
  to 
  

   this 
  release, 
  and 
  the 
  constant 
  inflow 
  from 
  the 
  pipes 
  maintains 
  the 
  

   supersaturation 
  of 
  the 
  volume 
  of 
  water 
  in 
  the 
  aquarium 
  to 
  very 
  nearly 
  

   that 
  of 
  the 
  water 
  in 
  the 
  pipes. 
  

  

  The 
  gill 
  apparatus 
  of 
  fishes, 
  for 
  the 
  osmotic 
  interchange 
  of 
  gases 
  

   which 
  keeps 
  the 
  blood 
  purified, 
  is 
  adjusted 
  to 
  water 
  in 
  which 
  the 
  gases 
  

   are 
  dissolved 
  at 
  atmospheric 
  pressure. 
  In 
  this 
  supersaturated 
  aqua- 
  

   rium 
  water 
  an 
  extraordinaril}^ 
  high 
  osmotic 
  pressure 
  exists 
  at 
  the 
  gill 
  

   membrane. 
  On 
  the 
  inside 
  of 
  this 
  membrane 
  the 
  blood 
  stream 
  tends 
  

   toward 
  a 
  supersaturation 
  equal 
  to 
  that 
  of 
  the 
  water 
  on 
  the 
  outside. 
  

   Two 
  chief 
  factors 
  are 
  then 
  conceived 
  to 
  operate 
  to 
  separate 
  the 
  air 
  

   from 
  solution, 
  one 
  being 
  the 
  temperature 
  of 
  the 
  systemic 
  blood, 
  the 
  

   other 
  the 
  mechanical 
  effect 
  of 
  the 
  surface 
  of 
  the 
  vessels 
  and 
  of 
  the 
  

   corpuscles. 
  

  

  The 
  oxidation 
  which 
  is 
  constantly 
  taking 
  place 
  within 
  the 
  blood 
  

   must 
  determine 
  a 
  higher 
  temperature 
  in 
  the 
  blood 
  than 
  in 
  the 
  water 
  

   surrounding 
  the 
  fish. 
  This 
  has 
  been 
  shown 
  by 
  observation 
  to 
  be 
  the 
  

   fact 
  for 
  certain 
  marine 
  fishes, 
  the 
  difference 
  in 
  some 
  cases 
  amounting 
  

   to 
  several 
  degrees. 
  The 
  blood 
  must 
  be 
  cooled 
  as 
  it 
  passes 
  through 
  the 
  

   gills 
  and 
  receives 
  its 
  supph^ 
  of 
  air, 
  and 
  the 
  subsequent 
  elevation 
  of 
  

   temperature 
  must 
  cause 
  some 
  of 
  the 
  air 
  to 
  come 
  out 
  of 
  solution 
  and 
  

   appear 
  in 
  the 
  blood 
  sti-eam 
  as 
  free 
  bubbles. 
  In 
  a 
  liquid 
  supersaturated 
  

   with 
  gas, 
  contact 
  with 
  a 
  solid 
  surface 
  causes 
  some 
  of 
  the 
  gas 
  to 
  deposit 
  

   in 
  bubbles 
  on 
  this 
  surface. 
  The 
  vascular 
  and 
  corpuscular 
  surfaces 
  

   therefore 
  probably 
  add 
  to 
  the 
  tendency 
  of 
  the 
  gas 
  to 
  come 
  out 
  of 
  solu- 
  

   tion. 
  The 
  process 
  continues 
  until 
  the 
  inevitable 
  mechanical 
  stoppage 
  

   of 
  the 
  circulation 
  occurs. 
  

  

  With 
  the 
  advent 
  of 
  the 
  flat-fish 
  season 
  nearly 
  ripe 
  fish 
  began 
  to 
  

   arrive 
  at 
  the 
  station, 
  to 
  be 
  held 
  in 
  wooden 
  tanks 
  until 
  spawning 
  

   occurred. 
  The 
  first 
  lot 
  of 
  these 
  fish, 
  a 
  small 
  number, 
  being 
  in 
  the 
  sta- 
  

   tion 
  water, 
  were 
  killed 
  by 
  it 
  like 
  the 
  aquarium 
  fish, 
  as 
  was 
  expected, 
  

  

  