428 Chemical Differentiation of the Brain 



as their instability towards heat, 6 lend support to this idea. They prob- 

 ably occur largely in the cytoplasm, cell body and its branches, where they 

 may act as oxygen carriers, as has been suggested by the work of Koch 

 and Mostrom. 7 



Cerebrosides. 



Chemistry. Complex combinations of fatty acids, galactose, and possi- 

 bly other hexoses with a nitrogen complex of the nature of sphingosine. 

 The cerebrosides are calculated from the lipoid sugar on the assumption 

 that they yield on hydrolysis 21.8 per cent of reducing sugar, the amount 

 found by Thierfelder in his cerebron. Correction must be made for the 

 cerebrin content of the sulphatides. 8 



Anatomical distribution. Although the cerebrosides are occasionally 

 met with in other tissues, they occur in largest amount in the medullated 

 nerve fiber, and their quantity increases as medullation proceeds. The 

 rather large amount found in the cortex 9 on chemical analysis indicates 

 that they may predominate in the fibers of that region. 



Physiological significance. As laid down in the medullated nerve fiber, 

 the cerebrosides most probably serve only a mechanical function and are 

 not available as sources of energy in spite of their carbohydrate and fatty 

 acid content. 



Sulphatides. 



Chemistry. These represent the combination of a phosphatide with a 

 cerebroside by means of a sulphuric acid group in ester combination. 10 

 The sulphatides are estimated from the lipoid sulphur on the basis of a 

 sulphur content of 2 per cent, based on the analysis of a purified compound. 11 



6 Koch, W and Koch, M. L. : this Journal, xiv, pp. 281-282, 1913. 



7 Koch, W and Mostrom, H. T. : Journ. of Pharm. and Exp. Ther., ii, No. 

 3, p. 265, 1910. 



8 Calculations for cerebrosides. The cerebrosides, from the lipoid frac- 

 tion, on hydrolysis for twenty-four hours with a weak solution of HC1 

 (75 cc. of water containing 3 cc. concentrated HC1), yield 21.8 per cent 

 by weight galactose. The calculations for cerebrosides were made on the 

 assumption that galactose and glucose were equivalent in reducing power 

 and the weight of galactose was thus determined from Munson and Walker's 

 tables for glucose. (Journ. Amer. Chem. Soc., xxviii, p. 663) . The corrected 

 weight of total galactose to cerebrosides was then made on the basis that 

 21.8 per cent of the latter is galactose. Finally since 42.9 per cent of the 

 sulphatides consist of cerebrosides this amount was deducted from the 

 total cerebrosides found. The difference was considered as cerebrosides. 



9 Koch, W. and Mann, S. A. : Archives of Neurology and Psychiatry, iv, 

 p. 33, 1909. 



10 Koch, W.: Zeitschr.f. physiol Chem., Ixx, p. 94, 1910. 



11 Calculations for sulphatides. These are considered to be of the gen- 

 eral formula: 



