The  Physiology  of  Stock-Breeding . 
77 
chicken  often  did  not  return  to  the  owner’s  yard  till  he  was  a 
second  season  bird.  He  might  then  very  likely  be  mated  with 
first  season  pullets,  which  would  not  be  quite  so  near  to  him  in 
blood  as  if  he  had  been  paired  with  birds  of  his  own  year  ; 
possibly  those  out  of  the  same  clutch  as  himself.  But  anyhow, 
the  belief  among  the  old-fashioned  “cockers”  in  the  advantage 
of  change  of  environment  was  great. 
Ovariotomy  and  the  Secretory  Functions 
OP  THE  Ovary. 
Besides  providing  the  germ  cells — ova  and  spermatozoa — 
the  ovaries  and  testes  serve  the  function  of  organs  of  internal 
secretion,  and  in  this  capacity  exert  an  influence  on  the  general 
bodily  metabolism.  The  nature  of  this  influence  is  best  shown 
by  the  results  of  castration  and  ovariotomy,  in  which  operations 
the  essential  organs  of  reproduction  are  removed. 
That  castration  in  the  male  if  performed  before  puberty 
arrests  the  development  of  many  of  the  secondary  sexual 
characters  is  well  known.  Thus,  in  horned  sheep,  after 
removal  of  the  testes  in  early  life,  the  shape  of  the  horns  is 
similar  to  that  of  the  female.  If,  however,  castration  is  delayed 
until  after  sexual  maturity  has  been  reached,  and  the  secondary 
male  characters  have  been  acquired,  the  changes  produced  are 
far  less  pronounced.  In  a similar  way  animals  which  are 
castrated  young  do  not  experience  sexual  desire,  but  this 
result  does  not  necessarily  follow  if  the  operation  is  carried 
out  later  in  life. 
The  erection  of  the  penis  in  all  animals  is  a complex  action, 
partly  muscular  and  partly  nervous,  under  the  control  of  a 
centre  located  in  the  hind  part  of  the  spinal  cord,  from  which 
impulses  are  transmitted  to  the  organ  in  question  by  certain 
nerves  called  by  physiologists  the  nervi  erigentes.  On  stimu- 
lating these  nerves  artificially  by  an  electric  current,  the  penis 
can  be  caused  to  erect  experimentally.  Dr.  Sutherland  Simpson 
and  I have  shown'  that  in  animals  that  have  been  castrated 
previous  to  puberty,  stimulation  of  the  nervi  erigentes,  if 
cari’ied  out  after  adult  age  has  been  reached,  does  not  produce 
erection,  thus  showing  that  in  the  absence  of  the  testes,  the 
mechanism  of  erection  is  not  developed. 
If  in  the  female  ovariotomy  or  the  removal  of  the  ovaries 
be  performed  after  sexual  maturity  has  been  reached,  the  uterus 
undergoes  a gradual  atrophy  ; if  the  removal  be  carried  out 
before  puberty,  the  uterus  remains  infantile  or  undeveloped. 
Mr.  Carmichael  and  I have  shown  that  on  the  other  hand,  if 
* Simpson  and  Marshall  : “ On  the  EfEect  of  Stimulating  the  Nervi 
Erigentes  in  Castrated  Animals,”  Quart.  Jour.  Exper.  Phys.,  Vol.  1,  1908. 
