Vol.. 7, 1921 
PHYSIOLOGY: OSBORNE AND MENDEL 
159 
mately 70 gm. have quadrupled their weight within the usual time, and 
appear as well nourished as companion rats on diets containing liberal 
portions of butter fat or lard, we cannot avoid the conclusion that if true 
fats are essential for nutrition during growth the minimum necessary 
must be exceedingly small. Drummond 3 has also secured some success 
on diets practically devoid of fat with rats receiving an approximate 
daily intake of neutral fat amounting to 14 mg. He too concludes that 
unless this minute amount of fat plays as important a r61e in the metabo- 
lism of the organism as do the minute quantities of such substances as the 
accessory factors, it is reasonable to suggest that pure fats are dispensable 
constituents of the mammalian diet. 
The outcome of all these investigations leads one to question seriously 
the contentions made, particularly during the recent war, that fats as 
such play some unique r61e in maintaining well-being; and further, as 
Maignon 4 supposes, that they play an important r61e in the utilization 
of protein, — a r61e which carbohydrates are powerless to fill. On the 
other hand the demonstrations afforded by our experiments should not 
be construed to minimize the great value of fats as a source of energy in 
the usual dietary, as well as their peculiar advantages in culinary pro- 
cedures. 
As we have recently pointed out 5 carbohydrates are ordinarily regarded 
as indispensable components of the food intake. This belief is based 
on the presence of more or less carbohydrate in the food mixtures con- 
sumed by man and the higher animals, and the fact that sugar is a con- 
stant constituent of the blood. It is almost universally taught that carbo- 
hydrate is essential for the proper metabolism of fats in addition to any 
other functions that it may perform in the body; for ketone substances 
may be excreted in diabetes when sugar fails to be burned up in the normal 
manner in the organism. On the other hand it is assumed that glucose 
can be formed from the protein molecule or its amino-acids under certain 
conditions in the metabolism so that one could conceive carbohydrate to 
become available for the special needs of fat metabolism and other purposes 
without being specifically furnished as preformed carbohydrate in the diet. 
The current opinion, summarized by one recent writer, 6 maintains that 
"carbohydrates are the most economical of the foodstuffs, both phys- 
iologically and financially. They are the greatest sparers of protein. 
Ingestion of fat has for its object the relieving of the intestine from ex- 
cessive carbohydrate digestion and absorption. Ingestion of fat in too 
large quantities leads to digestive disturbances, and if carbohydrates are 
entirely abandoned, to acetonuria." 
Not long ago we announced that rats receiving a diet in which the 
amount of digestible carbohydrate was at most exceedingly small can grow 
from an early age to adult size. The rations which we fed included pro- 
