being as low as 6 per cent, in
flounder, and in others as high as 30 per cent, in dried codfish. The
amount of fat, except in a few cases, as salmon and trout, is small.
Salmon is the richest in fat of any of the fishes. When salted and
preserved, the proportion of water is lessened and that of the nutrients
is increased. Fish can take the place of meat in the dietary, but it is
necessary to add a larger amount of fat to the ration because of the
deficiency of most fish in this ingredient. Fish has about the same
digestibility as meats. It is believed by many to be valuable because it
supplies a large amount of available phosphates. Analyses, however, show
that the flesh of fish contains no more phosphorus compounds than meats
in general, and its food value is due to protein rather than to
phosphates.[54]

Fish appears to be as completely and easily digested as meats.
Differences in flavor, taste, and palatability are due to small amounts
of flavors and extractive materials, varying according to the food
consumed by the fish and the conditions under which they lived. The
flesh of fish decays more readily than that of other meats and produces
ptomaines, or toxic substances, which are the result of fermentation
changes usually associated with putrefaction. Cases of poisoning from
eating unsound fish are not infrequent.[55]

Shellfish have about the same general composition as fish. In clams
there is a larger amount of dry matter than in oysters, which contain
about 12 per cent, half of which is protein. When placed in fresh water,
the oyster increases in size and undergoes the process known as
"fattening." Oftentimes impure water is used for this purpose, which
makes the eating of raw oysters a questionable practice from a sanitary
point of view, as the water in which they are floated often contains
disease-producing germs, as typhoid. During the process of fattening,
although the oyster increases in size and weight, it decreases in
percentage of nutrients. In discussing the composition of oysters,
Atwater states:[7]

"They come nearer to milk than almost any other food material as
regards both the amounts and relative proportions of nutrients."

139. Eggs, General Composition.--Eggs are a type of concentrated
nitrogenous food. About 75 per cent (shell removed) is water, about one
third is yolk, and a little over 50 per cent is albumin or white. The
shell makes up from 10 to 12 per cent of the weight. The yo