The  Physiology  of  Stock-Breeding . 
71 
The  vitality  of  spermatozoa  varies  in  different  species.  In 
the  rabbit  I have  found  living  spermatozoa  in  the  male  passage 
ten  days  after  castration,  but  they  have  not  been  kept  alive 
outside  the  body  for  so  long  a time.  By  maintaining  a tempera- 
ture equal  to  that  of  the  body,  and  after  adding  normal  salt 
Fig.  3.— Spermatozoon  of  ram  (very  highly  magnifled.) 
solution  or  Ringer’s  fluid  to  the  semen,  I have  succeeded  in 
keeping  spermatozoa  alive  for  twenty-four  hours,  but  not  for  a 
longer  period.  Iwanofl;,^  of  St.  Petersburg,  has  been  successful 
in  artificially  inseminating  mares  after  keeping  the  stallions’ 
spermatozoa  for  a short  time  in  various  artificial  media,  the 
mares  becoming  pregnant  and  producing  normal  foals.  These 
experiments  are  not  without  interest,  in  view  of  the  fact  that 
the  artificial  injection  of  semen  into  the  vagina  or  uterus  of 
female  animals  is  now  extensively  practised,  being  found  espe- 
cially useful  as  a means  of  overcoming  certain  forms  of  barren- 
ness, such  as  those  arising  from  a constricted  entrance  to  the 
uterus,  or  the  presence  of  an  abnormal  acid  vaginal  secretion 
which  has  the  effect  of  killing  the  spermatozoa  before  they  can 
effect  an  entrance  into  the  uterus.  Whether  spermatozoa  are 
capable  of  living  for  as  long  a time  in  the  female  genital  passages 
as  in  the  male,  is  a point  which  has  never  been  determined  (at 
least  for  the  domestic  animals).  It  may,  however,  be  pointed 
out  that  while  these  organisms  are  retained  in  the  male  they 
are  in  a condition  of  relative  quiescence,  and  that  there  are 
reasons  for  believing  that  they  do  not  become  actively  motile 
until  ejection  ; and  moreover  that  a state  of  constant  motility  is 
unfavourable  to  a long  continued  existence  unless  there  is  some 
means  of  renewing  the  supply  of  energy,  and  of  this  there  is  no 
evidence  in  the  case  of  living  spermatozoa. 
Factors  in  Fertility. 
Although  only  a small  number  of  ova — and  often  only 
one — are  sufficiently  mature  to  be  discharged  from  the  ovaries 
at  any  one  period  of  oestrus,  the  total  number  of  unripe  ova 
existing  in  those  organs  is  very  large,  but  most  of  these  are  in 
a very  immature  condition.  Each  ovum  is  contained  within  a 
follicle  or  vesicle,  and  the  follicles  vary  in  size  and  position  in 
the  ovaries  according  to  their  degree  of  development ; the 
smallest  lie  close  to  the  surface,  but  as  they  grow  bigger  they 
pass  inwards,  while  the  largest  follicles,  on  the  other  hand, 
protrude  visibly  from  the  surface,  and  each  one  occupies  a 
^ IwanofE  : “ De  la  Fecondation  Artificielle  chez  les  Mammiferes,”  Arch, 
des  Sciences  Biolugiques,  Vol.  12,  1907. 
