242
JOHN C. DITTMER
of analysis used does not make any allowance for the occurrence of
phospholipids different from the classic types and that the cephalin
fraction is a mixture of probably no less than six different kinds of
phospholipids. Important differences between species may be concealed
within the data available.
As can be seen, there is usually little variation in the distribution of
lecithin and cephalin in the brain of species in the same class. A striking
exception is the over-all low level of phospholipid in the brain of the
bowfin. No such generalization can be made about sphingomyelin.
Although, with the exception of the fishes studied, the level of sphingomyelin does not vary greatly within each class, the concentrations in
the various classes show a definite trend. The level in the brain of
mammals is significantly higher than that found in most of the fishes
and in the limited number of amphibians, reptiles, and birds studied.
In agreement with this, Bieth and Mandel (44) found that the sphingomyelin concentration in the brain of one species each of fish (carp),
tortoise, duck, fowl and of guinea pig, rat, cat, dog, and man increased
in the order given. A similar but not as striking pattern is observed in
the distribution of the phospholipids of spinal cord (Table II). It is
interesting to note that the proportion of sphingomyelin in the phospholipids of the nervous tissue of invertebrates (Table III) is even lower
than the proportion found in the submammalian vertebrates. In the
honeybee, for which the data are directly comparable to the data in
Table I, the level of sphingomyelin is also lower.
Before arriving at any final conclusions, one further aspect of the
problem must be considered. At an early age the brain and other
nervous tissues undergo myelinization. During this period the concentration of the phospholipids increases two- to threefold on the basis of
wet weight. Of particular interest, however, is the much more rapid
increase of sphingomyelin, a seven- to tenfold increase (41, 45). Patterson et dl. (43) noted that the phospholipid composition of the central
nervous system of the bee was very similar to that of vertebrates before
myelination, and McColl and Rossiter (38) have discussed the phospholipid concentration of invertebrate nervous tissue relative to the absence
or presence of a myelin sheath. Certain differences between the sphingomyelin concentration of brain cortex and the more heavily myelinated
white matter of brain of infants and adults have also been pointed out
(22, 45). It appears very likely that variations in phospholipid content of
the brain of different species may be directly related to the relative
amounts of certain cellular structures.
Although no comparative data are available, the fatty acid and
fatty aldehyde composition of several brain phospholipid fractions have
JOHN C. DITTMER
of analysis used does not make any allowance for the occurrence of
phospholipids different from the classic types and that the cephalin
fraction is a mixture of probably no less than six different kinds of
phospholipids. Important differences between species may be concealed
within the data available.
As can be seen, there is usually little variation in the distribution of
lecithin and cephalin in the brain of species in the same class. A striking
exception is the over-all low level of phospholipid in the brain of the
bowfin. No such generalization can be made about sphingomyelin.
Although, with the exception of the fishes studied, the level of sphingomyelin does not vary greatly within each class, the concentrations in
the various classes show a definite trend. The level in the brain of
mammals is significantly higher than that found in most of the fishes
and in the limited number of amphibians, reptiles, and birds studied.
In agreement with this, Bieth and Mandel (44) found that the sphingomyelin concentration in the brain of one species each of fish (carp),
tortoise, duck, fowl and of guinea pig, rat, cat, dog, and man increased
in the order given. A similar but not as striking pattern is observed in
the distribution of the phospholipids of spinal cord (Table II). It is
interesting to note that the proportion of sphingomyelin in the phospholipids of the nervous tissue of invertebrates (Table III) is even lower
than the proportion found in the submammalian vertebrates. In the
honeybee, for which the data are directly comparable to the data in
Table I, the level of sphingomyelin is also lower.
Before arriving at any final conclusions, one further aspect of the
problem must be considered. At an early age the brain and other
nervous tissues undergo myelinization. During this period the concentration of the phospholipids increases two- to threefold on the basis of
wet weight. Of particular interest, however, is the much more rapid
increase of sphingomyelin, a seven- to tenfold increase (41, 45). Patterson et dl. (43) noted that the phospholipid composition of the central
nervous system of the bee was very similar to that of vertebrates before
myelination, and McColl and Rossiter (38) have discussed the phospholipid concentration of invertebrate nervous tissue relative to the absence
or presence of a myelin sheath. Certain differences between the sphingomyelin concentration of brain cortex and the more heavily myelinated
white matter of brain of infants and adults have also been pointed out
(22, 45). It appears very likely that variations in phospholipid content of
the brain of different species may be directly related to the relative
amounts of certain cellular structures.
Although no comparative data are available, the fatty acid and
fatty aldehyde composition of several brain phospholipid fractions have