﻿388 
  JOHN 
  RENNIE. 
  

  

  The 
  principal 
  islet, 
  where 
  it 
  exists, 
  is 
  on 
  this 
  view 
  to 
  be 
  

   regarded 
  as 
  a 
  distinct 
  organ, 
  the 
  others 
  as 
  supplementary 
  

   bodies 
  of 
  similar 
  function. 
  In 
  those 
  cases, 
  viz. 
  certain 
  

   fishes 
  and 
  all 
  higher 
  animals, 
  where 
  it 
  is 
  presumably 
  absent 
  

   this 
  organ 
  in 
  the 
  course 
  of 
  phylogeny 
  has 
  disappeared 
  and 
  

   the 
  supplementary 
  bodies 
  have 
  increased 
  in 
  numbers 
  and 
  

   importance. 
  

  

  Histology. 
  

  

  The 
  material 
  made 
  use 
  of 
  for 
  histological 
  purposes 
  was 
  

   fixed 
  immediately 
  after 
  death, 
  in 
  either 
  corrosive 
  sublimate 
  

   or 
  Bles's 
  fluid. 
  After 
  washing 
  (in 
  the 
  case 
  of 
  the 
  sublimate) 
  

   and 
  dehydration, 
  the 
  tissue 
  was 
  embedded 
  in 
  paraffin 
  and 
  cut 
  

   serially 
  with 
  a 
  Cambridge 
  rocking 
  microtome. 
  The 
  sections 
  

   were 
  stained 
  with 
  liaBmatoxyliu 
  and 
  eosin 
  and 
  examined 
  under 
  

   a 
  Beck 
  microscope 
  possessing 
  a 
  -^-^ 
  oil 
  immersion 
  objective 
  

   as 
  well 
  as 
  lower 
  powers. 
  

  

  In 
  agreement 
  with 
  the 
  results 
  of 
  other 
  investigators, 
  the 
  

   tissue 
  of 
  these 
  islets 
  was 
  found 
  to 
  stain 
  a 
  lighter 
  tint 
  

   than 
  the 
  surrounding 
  pancreatic 
  alveoli. 
  Even 
  when 
  small 
  

   they 
  are 
  very 
  noticeable 
  as 
  paler 
  areas 
  in 
  the 
  pancreatic 
  

   mass; 
  they 
  are 
  frequently, 
  however, 
  more 
  massive 
  than 
  the 
  

   adjacent 
  organ, 
  from 
  which 
  they 
  are 
  definitely 
  separated 
  by 
  

   a 
  capsule. 
  They 
  are 
  an 
  epithelial 
  tissue 
  consisting 
  of 
  

   very 
  small 
  polyhedral 
  or 
  cylindrical 
  cells 
  well 
  supplied 
  with 
  

   blood-capillaries. 
  A 
  common 
  size 
  of 
  cell 
  is 
  about 
  10 
  jx 
  across 
  

   the 
  narrow 
  diameter. 
  

  

  In 
  a 
  number 
  of 
  instances 
  there 
  was 
  noted 
  a 
  difference 
  in 
  

   the 
  staining 
  capacity 
  of 
  different 
  areas 
  within 
  the 
  islets. 
  

   This 
  feature 
  has 
  been 
  noted 
  by 
  other 
  observers, 
  particularly 
  

   Massari 
  (12) 
  and 
  Diamare 
  (3). 
  The 
  latter 
  has 
  interpreted 
  it 
  

   as 
  indicating 
  a 
  difference 
  in 
  functional 
  state 
  of 
  different 
  

   parts 
  of 
  the 
  islet 
  ; 
  he 
  regards 
  such 
  appearances 
  as 
  the 
  accom- 
  

   paniment 
  of 
  different 
  phases 
  of 
  the 
  same 
  kind 
  of 
  cell. 
  

  

  fairly 
  frequent 
  occurrence 
  in 
  Lopliius. 
  These 
  appear 
  to 
  be 
  common 
  also 
  in 
  

   the 
  skate, 
  where 
  two 
  or 
  three 
  minute 
  examples 
  may 
  be 
  seen 
  in 
  a 
  single 
  fish. 
  

  

  