ON  THE  COMPOSITION  OF  THE  MUSCLES  OF  ANIMALS,  347 
this  alcoholic  solution  be  evaporated,  the  residue  is  a  sticky  mass 
of  an  amber-yellow  color,  which  is  completely  soluble  in  water. 
When  treated  with  sulphuric  acid,  it  is  decomposed  in  the  man- 
ner of  a  soap  ;  the  result  is  sulphate  of  soda  and  an  acid  which 
is  heavier  than  water.  This  acid  contains  phosphorus  and  ni- 
trogen, and  has  the  same  composition  as  Frerny's  oleophosphoric 
acid.  The  phosphuretted  fat  of  the  muscles  is  therefore  the 
same  as  that  of  the  brain,  and  it  is  diffused  in  the  most  various 
parts  of  the  organism  ;  it  diminishes  in  quantity  with  age,  and 
varies  according  to  the  species  of  animal. 
Thus,  the  fishes  with  soft  white  flesh,  such  as  the  carps,  plaice 
and  flounder,  contain  but  little  of  it ;  whilst  those  with  a  compact 
flesh,  with  a  distinct  taste,  which  are  generally  difficult  of  di- 
gestion, such  as  the  herring,  mackerel,  trout  and  especially  the 
salmon,  contain  it  in  considerable  quantity.  It  is  to  this  phos- 
phuretted fat  that  these  fishes  are  indebted  for  their  charac- 
teristic flavor. 
In  the  examination  of  the  muscles  of  these  fishes,  the  authors 
were  led  to  investigate  the  coloring  matter  of  the  muscles,  which 
is  so  remarkable  in  the  salmon,  the  salmon-trout,  and  some  other- 
species.  This  coloration  stands  in  determinate  relation  to  the 
reproduction,  for  the  salmon  has  red  flesh  throughout  the  year, 
but  it  becomes  paler  at  the  spawning  season ;  and  this  change  of 
color  is  still  more  distinct  in  the  trouts,  the  flesh  of  which  be- 
comes perfectly  white  at  that  period. 
As  the  fishes  do  not  all  spawn  at  the  same  time,  and  the  fe- 
males have  a  stronger  salmon  color  and  retain  it  longer  than  the 
males,  it  follows  that  we  may  obtain  from  the  same  water  trouts 
with  white  or  salmon  colored  flesb.  From  this  it  follows  also, 
that  the  salmon  trout  is  not  a  hybrid  between  the  salmon  and 
the  trout,  which  moreover  cannot  well  be  the  case,  as  the  salmon 
spawns  in  July,  rarely  even  in  August,  and  the  trout  in  Decem- 
ber. 
The  coloring  matter  of  the  flesh  of  the  salmon  has  already 
been  mentioned  by  Davy  in  his  «  Salmonia."  He  states  that 
the  muscles  of  the  salmon  may  be  deprived  of  their  color  by 
ether.  The  authors  have  found  that  this  coloring  matter  consists 
of  a  fat,  which  possesses  the  properties  of  a  weak  acid,  and  is 
dissolved  in  a  neutral  fat.    The  authors  call  this  body 
