There  are  two
kinds  of  corpus-
cles or  cells  visible
with  the  micro-
scope; namely,
the  red  and  the
white.  The  red
ones  are  bi-con-
cave  discs,  about
•j^o  of  an  inch  in
diameter.  They
are  often  seen  in
rolls  like  piles  of
coins.  The  num-
ber of  them  is  as-
tounding,  for
there  are  about
five  millions  in  a

cubic  millimeter  ^^'  ^^*  Human  blood-cells.  A,  rolls  of  red  cells
*  ui  A  /  \  •!  ^*^  *^®  white  cells  a.  B,  C,  D,  E,  various  views  of
01  DlOOa.  (A  mil-  red  ceUs.  F,  white  cell  magnified  same  as  D.  H,  7,
limeter  is  approx-  red  cells  covered  with  little  knobs  (abnormal,  due
;*v«»4-Al<tr  _l     ^*   ««      to  changes  after  blood  is  placed  on  object-slide).
miateiy  ts  oi  an     ^^^^  Huxley.)
inch   long;    com-
pute how  many  red  corpuscles  in  a  cubic  inch  of  blood.)
In  the  diseased  condition  known  as  anaemia,  which  is  char-
acterized by  the  whiteness  of  the  skin,  the  number  of  red
corpuscles  is  greatly  reduced.
The  red  color  of  these  blood-cells  is  due  to  a  substance
called  hcemoglobin,  which  is  most  important  in  the  blood's
work  of  carrying  oxygen  to  the  cells  of  the  body.
484  APPLIED  BIOLOGY

The  red  corpuscles  of  man  and  other  mammals  have  no
nuclei,  except  in  embryonic  stages ;  but  all  lower  vertebrates
—  birds,  reptiles,  amphibia,  and  fishes  —  have  nuclei  in  all
red  corpuscles,  even  in  the  adult  animals.  Scientists  have
not  yet  found  any  reason  for  this  difference.
It  is  also  interesting  to  know  that  red  corpuscles  are  con-
stantly being  formed  in  the  red  marrow  of  bones.  Obtain  a
long  bone  from  a  meat-market,  break  it  open,  and  examine
the  marrow.
