LIPIDS PRESENT IN BRAIN AND NERVOUS TISSUE 757 



lecithin, 7.05%; cephalin, 14.35%; sphingomyelin, 4.96%; total essen- 

 tial lipids, 48.62%; total lipids, 51. 59%. 



No important differences would appear to obtain in the distribution 

 of the lipids in the brain of the higher mammals similar to the variation 

 in cerebroside content noted with phylogenetic evolution. Moreover, 

 Blancher et a/. 299 noted that a significant amount of a hexaenoic acid is 

 present in the gray matter of both monkey and human brain, but is absent 

 from the white matter of both species. 



b. The Effect of Age on Brain Lipids, (a) The Corn-position during 

 Prenatal Development. Most workers have reported that cerebrosides are 

 lacking in the brain at birth; their appearance and their subsequent in- 

 crease parallel the development of the myelin sheath. Sphingomyelin, 

 another lipid component largely present in the myelin sheath, is one of the 

 last phospholipids to appear in the development of the brain and nervous 

 tissue. 



Backlin 300 reported the absence of cerebrosides from the rabbit brain at 

 birth. In the case of the human fetus, Schuwirth 301 found only traces of 

 cerebrosides and no sphingomyelin in the seventh and eighth months of 

 intrauterine life, and even at birth. 



Mihara 302 observed that cephalin made up the principal part of the cen- 

 tral nervous system of the early fetus. During the course of fetal growth, 

 lipids were shown to increase, while the total nitrogen decreased in the 

 cerebrum, medulla oblongata, and spinal cord. The greatest increase in 

 lipids occurred in the cerebrum. The most distinct changes in cholesterol 

 and cerebrosides did not occur until the last two months before term. 

 Bieth and Mandel 303 reported that, during the primary phase in the de- 

 velopment of the brain of the chick embryo, cephalin is the chief phos- 

 pholipid. Lecithins increase during the next stage, while sphingomyelins 

 appear last. 



(6) The Composition during Postnatal Development. During the ex- 

 trauterine development, the dry substance of the brain increases; the total 

 lipids constitute a greater portion of the dry matter, and all lipid fractions 

 are increased in terms of moist weight. 



As already indicated, the greatest increase occurs in the cerebrosides 



299 G. Blancher, E. Le Breton, and P. May, Compt. rend. soc. biol, 146, 219-222 (1952) 



300 E. Backlin, Beitrage zur quaniitativen Kenntnis derGehirnlipoide, Inaugural Disserta 

 tion, Almquist, Upsala, 1930; cited by W. R. Bloor, Biochemistry of the Fatty Acids 

 Reinhold, New York, 1943, p. 207. 



301 K. Schuwirth, Z. physiol. Chem., 263, 25-36 (1940). 



302 T. Mihara, /. Biochem. (Japan), 39, 155-161 (1952). 



303 R. Bieth and P. Mandel, Bull. soc. chim. biol, 32, 109-115 (1950). 



