THIRTEENTH ANNUAL MEETING. 177 
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pounds. Each of the three groups of nutrients probably shares, 
directly or indirectly, in the production of muscular force. So, 
too, it appears that the combustion which produces animal heat 
is not confined to the carbo-hydrates and fats, but the protein 
compounds, or the products of their decomposition, are also 
used for this purpose. Again, the production of fat in the body 
was formerly ascribed to the fats and carbo-hydrates alone. On 
the other hand some physiologists maintain that the carbo-hy- 
drates cannot be transformed into fats, and that a very large part 
of the fat of the body is formed from the disintegration of the al- 
buminoids. The weight of evidence to-day is decidedly in favor 
of the assumption that all three of the great classes of nutrients 
in our foods—the albuminoids, the carbo-hydrates, and the fats— 
are transformed into fat, and that the fat thus formed is con- 
sumed, either before or after being stored as body-fat. 
It appears, then, that protein is the most important constituent 
of our food, because, while it performs the functions of each of 
the other two chief nutrients in being transformed into fat and 
in being consumed for fuel, it has a most weighty office of its 
own in forming the basis of the blood and in building up the 
muscular and other nitrogenous tissues, an office which no other 
nutrient can perform at all. And, as we shall see further, in ex- 
amining the pecuniary cost, protein is the dearest as well as the 
most important of the ingredients of foods. 
Next in physiological importance to protein come the fats. 
They lack the nitrogen of the protein and cannot do the work of 
protein in forming nitrogenous tissue, making blood, muscle, etc. 
But they are very rich in carbon and hydrogen, more so than 
either protein or carbo-hydrates, and hence they have a very 
high value for fuel, to supply heat and probably muscular force. 
And in pecuniary cost as well as in physiological importance 
they rank between protein and carbo-hydrates. 
The carbo-hydrates stand lowest in the scale of physiological 
importance and are pecuniarily the least expensive. Neverthe- 
less it would be wrong to class the carbo-hydrates of food as on 
the whole of minor importance. They have a most important 
use in taking the place of protein and fats and protecting them 
from being consumed, just as the fats replace and thus save the 
