AmMav^w:arm'}      The  Nomenclature  of  the  Proteins.  231 
III.  The  sub-classes  should  be  as  follows  : — 
1.  Protamines.  These  are  simple  members  of  the  group.  They 
are  exemplified  by  substances  like  salmine  and  sturine  which  have 
been  separated  from  fish-sperm. 
2.  Histones.  These  are  more  complex  substances :  this  and  the 
previous  class  probably  pass  gradually  into  one  another.  The  class 
is  exemplified  by  the  histones  separated  by  Kosse]  from  blood-cor- 
puscles; precipitability  by  ammonia  is  one  of  their  distinguishing 
features. 
3.  Albumins.  These  are  proteins  of  which  egg-albumin  and 
serum-albumin  may  be  taken  as  typical  examples. 
4.  Globulins.  These  are  proteins  which  differ  from  the  albumins 
in  solubility ;  they  are  more  readily  "  salted  out "  of  solution  than 
the  albumins.  They  are  exemplified  by  serum-globulin  and  fibri- 
nogen. The  class  should  also  include  certain  derivatives  of  globulins 
such  as  fibrin  and  myosin. 
N.  B. — The  carbohydrate  radical  separable  in  small  quantities 
from  many  members  of  Classes  3  and  4  is  probably  not  to  be  con- 
sidered as  a  prosthetic  group,  as  it  is  in  the  gluco-proteins  (see 
below). 
N.  B. — It  appeared  advisable,  especially  from  the  teachers'  stand- 
point, to  introduce  a  general  term  to  include  proteins  coagulable 
by  heat  (Classes  3  and  4) ;  but  a  term  likely  to  meet  with  general 
acceptance  has  not  yet  been  suggested. 
5.  Sclero-proteins.  This  new  word  takes  the  place  of  the  word 
albuminoid  in  the  limited  sense  in  which  the  majority  of  physiolo- 
gists have  been  accustomed  to  use  it.  It  includes  such  substances 
as  gelatin  and  keratin ;  the  prefix  indicates  the  skeletal  origin  and 
often  insoluble  nature  of  its  members. 
6.  Phospho-proteins.  This  class  includes  such  substances  as 
vitellin  and  caseinogen  with  its  derivative  casein.  The  prefix 
nucleo,  frequently  used  in  relation  to  this  class,  is  incorrect  and 
misleading. 
7.  Conjugated  proteins.  These  are  substances  in  which  the 
protein  molecule  is  united  to  a  "  prosthetic  group."  The  principal 
sub-divisions  are : — 
(a)  Nucleo-proteins. 
(b)  Gluco-proteins  (e.  g.,  mucin). 
(c)  Chromo-proteins  (e.g.,  haemoglobin). 
