i2o THE CHEMISTRY OF THE TISSUES AND ORGANS. 
Midler 1 obtained cerebrin by rubbing brain up with baryta water, 
so as to form a milky fluid ; this is boiled, and the resulting coaguluin 
extracted with boiling alcohol ; on cooling, the alcoholic solution deposits 
cerebrin and cholesterin. The latter is removed by ether, and the former 
is purified by repeated crystallisation from boiling alcohol. According to 
MiiUer, its formula is C 17 1I ; X<> ; : according to Parens,' 2 C 80 H 160 N 2 O 15 . 
Parous also obtained two other similar substances (homocerebrin and 
encephalin) with different formula?. Adopting a slightly different modus 
operandi, Geoghegan 3 obtained a substance with the formula C 3y H 110 N 2 ( V, : ,. 
Thudichum 4 separated three cerebrins, which he named cerebrin 
(( ;1 ir, ;i; X 2 8 ), phrenosine 5 (C^H^NOg), and kerasine (C 4(i H, (1 X( _),,). 
Gamgee 6 found that, while protagon cannot be separated by the simple 
action of solvents into lecithin and cerebrin, yet such non-phosphorised 
substances do exist by its side in the brain, and one which he called 
pseudo-cerebrin (l\ 4 H, 12 XCO can lie obtained from protagon by the 
action of caustic baryta. 
The fact that the cerebrins are glucosides was known to Liebreich," 
Diaconow, Otto, 8 Geoghegan, and Thudichum, 10 but it was only within 
quite recent years that the sugar was identified as galactose, almost 
simultaneously in this country and in Germany. 11 
The most recent work on the subject is that by Kossel and Freytag, 12 
who adopt the very appropriate name of cerebrosides for these bodies. 
They find that these substances are constituents of the medullary 
sheaths rather than of the axis cylinders. They have especially worked 
at two, which they obtained by the decomposition of protagon crystals. 
namely, cerebrin and kerasin. The analyses of these agree very well 
with those previously published by Thudichum, Parens, and others. 
Their molecular weight was investigated by Beckmann's boiling method, 
and by the examination of their barium and bromine compounds. By 
treatment with nitric acid they yield not only galactose but also a 
fatty acid recognised as neurostearic acid by Thudichum, and correctly 
analysed but not identified by Muller. It is, in fact, stearic acid, three 
molecules of which are formed from cerebrin for every two atoms of 
nitrogen. From all these considerations, the formula given to cere- 
brin is C- ft H 140 X.>O r , and to kerasin (the homocerebrin of Parens), 
C 70 H 438 X 2 O 12 . 
Similar substances occur in other parts of the body: thus two 
separated from pus are named pyosin, 57 H U0 N 2 O 15 , or C- 8 H nil X.,< >,-, 
and pyogenin, C u .;H 12v X.,0 19 . These bodies and similar ones separated 
from testicular cells are components of the cell protoplasm, not of the 
nucleus (Kossel and Freytag). 
1 Ann. d. Ohem., Leipzig, Bd. ciii. S. 131 ; ev. S. 361. 
2 Journ. f. prakt. Ohem., Leipzig. Bd. exxxii. S. 310. 
3 Ztschr. f. physiol. Ohem., Strassburg, Bd. iii. S. 332. 
4 Loc. cii. 
5 For recent papers on phrenosine, see Thudichum, Journ. f. prakt. Ohem., Leipzig, 
Bd. liii. S. 49 ; Kossel, ibid., 1896, Bd. liv. S. 215. 
e Loc. cif. 
7 Virchoic's Archie, Bd. xxxix. S. 183. 
8 Ibid., Bd. xli. S. 272. 
9 Geoghegan stated that the reducing substance had the formula C 22 H 45 5 ; he termed 
it cetylid ; cetylid was no doubt a mixture of galactose and fatty acids. 
10 Journ. f. prakt. Chem., Leipzig, Bd. xxv. S. 23. 
11 Thierfelder, Ztschr. f. physiol. Ohem., Strassburg, Bd. xiv. S. 209; Brown and 
Morris. Proc. Chem. Soc. London, 1S89, p. 167. 
12 Ztschr. f. physiol. Ohem., Strassburg, Bd. xvii. S. 431. 
