90
F. B. SHORLAND
stituents of the diet. Grass-fed carp, for example, deposit diene and
triene acids characteristic of grass lipids, but which are not found elsewhere in aquatic life (350). Similarly, eels fed a diet of herring flesh
modify their depot fats to resemble more closely those of herrings (351).
In addition mullet (Mugil cephalus) when fed a "fat free" diet are to
a large extent depleted of their reserves of polyunsaturated acids. On
addition of menhaden oil to the diet, the polyunsaturated acids are deposited in the same proportions as fed. Similarly, in mullet fed a commercial cooking fat made from cottonseed oil, the depot fats again resemble the dietary fat (352).
In the next stage, represented by amphibians, reptiles, and nonruminants, the dietary carbohydrate and protein is used to produce
endogenous fat. Such fat consists mainly of palmitic (about 27-30%)
and oleic acids with lesser amounts of stearic, myristic, and palmitoleic
acids. In addition, as in fishes, the dietary fats are also deposited so
that the depot fats now consist of a mixture of endogenous and
exogenous fats. The composition of the depot fat will now depend on
the nature and amount of the dietary fat, and on the rate of growth, as
suggested by Callow (353) provided the diet, as in coconut oil, does
not contain lower fatty acids that are rapidly metabolized.
Finally, in ruminants the depot fats are formed largely from the
acetate and lower volatile fatty acids produced in the rumen from carbohydrates and proteins which are broken down by the action of the
microorganisms. The dietary fat appears to have little influence on the
composition of the depot fat. This is because the dietary unsaturated
fatty acids, such as linolenic acid, are hydrogenated to form saturated
acids along with lesser amounts of monounsaturated and traces of diunsaturated acids, which are trans and positional isomers of oleic and
linoleic acids (118-121).
D. FATTY ACIDS OF WAXES, PHOSPHOLIPIDS, AND RELATED SUBSTANCES
AND THE CLASSIFICATION OF ORGANISMS
The depot fats of plants and animals have been shown to vary in
the types and proportions of fatty acids. These variations may indicate
some degree of differentiation in organisms in different parts of the
phylogenetic scale. As disclosed in Section VII,C above, however, the
differentiation exhibited in animal depot fats is, to a considerable extent, fortuitous and dependent on the dietary fat. In the depot fats of
plants, including those of cryptogams and seed fats, the differentiation
in fatty acid types and composition sometimes appears to be characteristic of the species, genus, or family.
The limited data on the fatty acids of plant waxes have not shown
F. B. SHORLAND
stituents of the diet. Grass-fed carp, for example, deposit diene and
triene acids characteristic of grass lipids, but which are not found elsewhere in aquatic life (350). Similarly, eels fed a diet of herring flesh
modify their depot fats to resemble more closely those of herrings (351).
In addition mullet (Mugil cephalus) when fed a "fat free" diet are to
a large extent depleted of their reserves of polyunsaturated acids. On
addition of menhaden oil to the diet, the polyunsaturated acids are deposited in the same proportions as fed. Similarly, in mullet fed a commercial cooking fat made from cottonseed oil, the depot fats again resemble the dietary fat (352).
In the next stage, represented by amphibians, reptiles, and nonruminants, the dietary carbohydrate and protein is used to produce
endogenous fat. Such fat consists mainly of palmitic (about 27-30%)
and oleic acids with lesser amounts of stearic, myristic, and palmitoleic
acids. In addition, as in fishes, the dietary fats are also deposited so
that the depot fats now consist of a mixture of endogenous and
exogenous fats. The composition of the depot fat will now depend on
the nature and amount of the dietary fat, and on the rate of growth, as
suggested by Callow (353) provided the diet, as in coconut oil, does
not contain lower fatty acids that are rapidly metabolized.
Finally, in ruminants the depot fats are formed largely from the
acetate and lower volatile fatty acids produced in the rumen from carbohydrates and proteins which are broken down by the action of the
microorganisms. The dietary fat appears to have little influence on the
composition of the depot fat. This is because the dietary unsaturated
fatty acids, such as linolenic acid, are hydrogenated to form saturated
acids along with lesser amounts of monounsaturated and traces of diunsaturated acids, which are trans and positional isomers of oleic and
linoleic acids (118-121).
D. FATTY ACIDS OF WAXES, PHOSPHOLIPIDS, AND RELATED SUBSTANCES
AND THE CLASSIFICATION OF ORGANISMS
The depot fats of plants and animals have been shown to vary in
the types and proportions of fatty acids. These variations may indicate
some degree of differentiation in organisms in different parts of the
phylogenetic scale. As disclosed in Section VII,C above, however, the
differentiation exhibited in animal depot fats is, to a considerable extent, fortuitous and dependent on the dietary fat. In the depot fats of
plants, including those of cryptogams and seed fats, the differentiation
in fatty acid types and composition sometimes appears to be characteristic of the species, genus, or family.
The limited data on the fatty acids of plant waxes have not shown