AmseJp°tur'i92iarm*}       The  Relative  Value  of  Proteins:  651 
QUALITY  OF  PROTEIN  IN  MILK  PRODUCTION. 
Diet  plays  a  large  part  in  milk  production.  Quantity  and  quality 
of  protein  are  the  chief  factors.  Since  neither  the  animal  body  nor 
the  mammary  gland  can  synthesize  amino-acids,  the  food  must  con- 
tain sufficient  for  the  manufacture  of  casein  and  lactalbumin.  Hart 
and  Humphrey  have  paid  some  attention  to  this  question.  A  high 
milk  yield  of  27  lb.  requires  a  protein  ration  1  :  4.5 ;  1  :  6.7  is  neces- 
sary for  11  lb.;  1:8.5  is  n°t  economical.  If  the  animal  is  not 
furnished  with  sufficient  protein  it  produces  milk  from  its  own  tis- 
sues. Skim  milk  has  an  efficiency  of  65,  against  25  of  a  mixture  of 
maize  and  alfalfa.  Gluten  feed  (maize  embryo)  has  45,  flax  seed 
61,  casein  59,  milk  powder  60.  A  comparison  of  clover  and  alfalfa 
on  the  same  basal  diet  showed  a  superiority  of  alfalfa  for  high 
milk  production  for  16  weeks.  With  another  basal  diet  the  reverse 
may  be  the  case.  The  value  will  depend  on  the  proportions  of  the 
amino-acids  in  the  food  and  their  correspondence  to  the  proportions 
in  the  milk  proteins.  No  guide  is  at  present  available  from  the  side 
of  chemical  analysis.  Little  is  known  of  the  proteins  of  grasses  and 
green  foods.  The  nearest  approach  to  the  proteins  of  cow's  milk  are 
the  proteins  contained  in  the  milk  of  other  animals.  If  the  milk 
proteins  of  all  animals  are  the  same  in  composition,  the  milk  of  one 
animal  will  be  as  good  as  that  of  another  animal,  but  if  not,  as  is 
most  likely,  the  best  source  is  the  animal's  own  milk.  Cannibalism 
has  been  proved  to  be  the  best  method  of  feeding  dogs.  We  ap- 
proach cannibalism  in  the  nursing  of  the  young  on  mother's  milk. 
Milk  contains  ultimately  the  proteins  of  the  mammary  gland. 
PROTEINS  AND  PELLAGRA. 
The  primary  cause  of  the  disease  pellagra  appears  to  be  quality 
of  protein,  but  at  the  same  time  insufficiency  of  protein  together 
with  improper  salt  supply  may  play  a  part. 
Pellagra  was  not  recorded  in  Europe  before  the  introduction  of 
maize  into  Spain  by  Columbus.  The  disease  spread  to  France, 
Lombardy  and  eastwards,  wherever  maize  was  extensively  used  for 
food.  Roussel  (1866)  cured  it  by  good  food,  and  advanced  cases 
have  been  successfully  treated  by  a  generous  diet  (Lorentz,  1914; 
Willets,  1915).  Goldberger  cured  and  prevented  the  seasonal  ap- 
pearance of  pellagra  in  lunatic  asylums  by  increasing  the  meat  and 
milk  in  the  diet,  which  had  previously  been  very  deficient  in  this 
