1. FATTY ACID OCCURRENCE AND DISTRIBUTION
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the school shark (Galeorhinus australis MacLeay) (161), in which the
liver is the main fat depot, the head and body oils are not appreciably
different in fatty acid composition from the liver oils.
In the sperm whale, the main fat reserves are in the head and the
blubber and are present largely as esters of higher fatty alcohols. The
unsaturation is almost confined to the monoethenoid state, and the
average molecular weight of the fatty acids is lower than in ordinary
whale oil. The relative absence of C 22 acids is noteworthy (167). The
partial analysis of sperm whale liver oil by Tsujimoto and Kimura (314)
suggests that this depot has a fatty acid composition of the normal
marine type. In the porpoise and the dolphin the main depots, including
the head, body, and jaw, contain considerable proportions of isovaleric acid, together with unusually high proportions of C 14: and Ci 6
acids. These unusual features are absent from the organ fats, the composition of which corresponds more closely to that of typical marine
fat (168) (see Table XXII).
The depot fats of land animals also show variations in composition
according to site of deposition. However, no appreciable variations in
fatty acid composition are observed between the abdominal, neck, and
gizzard fats of the hen (179).
To explain the relatively high content of fully saturated glycerides
in ruminant depot fats especially, Hilditch (3) has suggested that such
fats are assembled to begin with on an even-distribution pattern, as in
other plant and animal fats. Subsequently the preformed oleoglycerides
are hydrogenated in situ to give fully saturated glycerides. In accordance
with this suggestion it has become widely accepted that the differences
between the internal fats, such as kidney fat, and external fats, such as
outer back fat, rest on their respective contents of oleic and stearic
acids. The analytical data published have also hitherto supported this
view. In passing from the kidney fat to the outer back fat it is found, as
a rule, that the percentage of oleic acid rises, while that of stearic falls.
The other major constituent, palmitic acid, remains fairly constant.
This is illustrated in Table XXIII showing the changes in composition
of the depot fats of pigs with site of deposition. In the liver fat there is
a further change in composition with the appearance of C 20 and C 22 unsaturated acids, while in the bone fat the amount of palmitic acid falls
below the more or less constant level of 25-30% characteristic of the
main depot fats.
Recently Dahl (317), from a survey of the composition of the
depot fats of farm animals, considered that the changing properties of
animal fats as we proceed from the internal to the external depots arise
differently in different animals. In pigs, the difference between the peri-
67
the school shark (Galeorhinus australis MacLeay) (161), in which the
liver is the main fat depot, the head and body oils are not appreciably
different in fatty acid composition from the liver oils.
In the sperm whale, the main fat reserves are in the head and the
blubber and are present largely as esters of higher fatty alcohols. The
unsaturation is almost confined to the monoethenoid state, and the
average molecular weight of the fatty acids is lower than in ordinary
whale oil. The relative absence of C 22 acids is noteworthy (167). The
partial analysis of sperm whale liver oil by Tsujimoto and Kimura (314)
suggests that this depot has a fatty acid composition of the normal
marine type. In the porpoise and the dolphin the main depots, including
the head, body, and jaw, contain considerable proportions of isovaleric acid, together with unusually high proportions of C 14: and Ci 6
acids. These unusual features are absent from the organ fats, the composition of which corresponds more closely to that of typical marine
fat (168) (see Table XXII).
The depot fats of land animals also show variations in composition
according to site of deposition. However, no appreciable variations in
fatty acid composition are observed between the abdominal, neck, and
gizzard fats of the hen (179).
To explain the relatively high content of fully saturated glycerides
in ruminant depot fats especially, Hilditch (3) has suggested that such
fats are assembled to begin with on an even-distribution pattern, as in
other plant and animal fats. Subsequently the preformed oleoglycerides
are hydrogenated in situ to give fully saturated glycerides. In accordance
with this suggestion it has become widely accepted that the differences
between the internal fats, such as kidney fat, and external fats, such as
outer back fat, rest on their respective contents of oleic and stearic
acids. The analytical data published have also hitherto supported this
view. In passing from the kidney fat to the outer back fat it is found, as
a rule, that the percentage of oleic acid rises, while that of stearic falls.
The other major constituent, palmitic acid, remains fairly constant.
This is illustrated in Table XXIII showing the changes in composition
of the depot fats of pigs with site of deposition. In the liver fat there is
a further change in composition with the appearance of C 20 and C 22 unsaturated acids, while in the bone fat the amount of palmitic acid falls
below the more or less constant level of 25-30% characteristic of the
main depot fats.
Recently Dahl (317), from a survey of the composition of the
depot fats of farm animals, considered that the changing properties of
animal fats as we proceed from the internal to the external depots arise
differently in different animals. In pigs, the difference between the peri-