It  is  asserted  that  this  action  of  carbohydrates  ia
explained  by  the  fact  that  these  nutrients  have  a  greater
affinity  for  oxygen  than  proteids  and  so  are  the  first  to  undergo
oombustion.
The  term  albaminoid  was  formerly  nsed  as  synonymous
irith  proteid,  but  is  now  employed  to  include  nitrogenous
bodies  (gelatin)  derived  from  protein  in  the  body  but  not
oonvertible  into  proteids.  These  bodies  do  not  take  the
place  of  proteids,  but  appear  to  fulfil  the  functions  of  circu-
lating protein,  and,  lilce  carbohydrates,  conserve  protein
oonsumption,  but  are  not  tissue  bnilders.
Carbohydrates  aid  directly  in  the  production  of  fat.
Fat  in  the  food  may  be  directly  assimilated  as  such  if  there
is  a  sufficient  carbohydrate  and  proteid  ration  to  protect  it
from  decomposition.  The  rdle  carbohydrates  play  includes :

1.  The  formation  of  tissue  indirectly  by  protecting  the
"proteid  elements  from  combustion  with  an  insufficient
nitrogenous  diet

2.  The  generation  of  heat,  energy,  or  mechanical  work.
3.  The  production  of  fat.
Carbohydrates  cannot  be  relied  upon  as  sole  articles  of
food.  The  fat  of  the  body  is  derived  from  the  decomposition
of  proteids  and  carbohydrates,  and  directly  from  fat  con-
tained in  the  food.  Fat  lubricates  the  tissues,  and  a  reason-
able accamnlation  serves  as  a  store  of  potential  energy  to  be
called  upon  in  time  of  need,  when  its  action  is  similar  to  that
of  carbohydrates.  The  main  source  of  muscular  energy,
movement,  or  mechanical  work,  is  thought  to  reside  in  the
carbohydrates,  because  with  excessive  muscular  work  there
is  increased  evolution  of  heat,  carbonic  dioxide  and  water,
but  no  material  increase  in  excretion  of  nitrogen  in  the  urine.
