238 ANIMAL FATS AND PHOSFHATIDES. 



Various methods have been suggested by STRECKER, HOPPE-SEYLER 

 and DIACONOW, THUDICHUM, GILSON, ZUELZER and BERGELL l for the 

 preparation of the lecithins. As none of these yields a positively pure 

 product we will only here mention them. According to ERLANDSEN'S 

 experience all methods which are based upon the precipitation of the 

 lecithin as a metallic compound should be avoided. The best method 

 depends upon the solubility of the lecithin in alcohol and in ether in the 

 cold and its precipitation by acetone (ERLANDSEN, H. E. ROAF and E. 

 EDIE 2 ) . The work of ERLANDSEN is especially referred to in the prepara- 

 tion of lecithins. 



For the present we have no quantitative method for estimating 

 lecithin. The methods used in the past, when the amount of lecithin was 

 calculated from the amount of phosphorus contained in the alcohol-ether 

 extract is useless, as in this case the phosphorous content of all the 

 phosphatides is determined and not alone of the lecithins. Even the detec- 

 tion of choline is not evidence, as this base probably also occurs in other 

 phosphatides. In the detection of choline the double platinum compound 

 is ordinarily prepared, and this can be done as described below. In 

 special determinations of lecithin and cephalin KOCH used to heat with 

 hydroiodic acid, and determined the methyl groups split off below 240 

 and those at about 300. Instead of this he recommends with WOODS 3 

 to separate the two by precipitation in alcoholic solution, while boiling, 

 with alcoholic lead acetate solution and a little ammonia, which precip- 

 tates only the cephalin. 



Cephalin is also a monoamidophosphatide whose formula, based upon 

 the investigations of THUDICHUM and Kocn, 4 is probably C42H 8 2NPO 13 . 

 For the present cephalin must be classified with the lecithin group. The 

 views of these two investigators as to the constitution of this body, 

 which is difficult to purify, differ very considerably. According to THUDI- 

 CHUM, on cleavage it yields neurine, glycerophosphoric acid, stearic acid, 

 and a specific fatty acid, cephalic acid. According to KOCH it contains, on 

 the contrary, only one methyl group attached to nitrogen, and is therefore 

 probably dioxystearylmonomethyl lecithin, while according to COUSIN 5 

 it yields, like lecithin, stearic acid, an unsaturated fatty acid, glycero- 

 phosphoric acid and choline as decomposition products. Cephalin is 

 amorphous and swells up in water like lecithin. It is soluble in cold 

 ether, glacial acetic acid, and chloroform, but is insoluble in acetone and 

 in alcohol, either cold or warm. The alcoholic solution, as previously 



1 Strecker, Annal. d. Chem. u. Pharm., 148; Hoppe-Seyler and Diaconow, 1. c.; 

 Thudichum, 1. c.; Gilson, Zeitschr. f. physiol. Chem., 12; Zuelzer, ibid., 27; Bergell, 

 Ber. d. d. chem. Gesellsch., 33. 



2 Erlandsen, 1. c.; Roaf and Edie, Thompson Yates Laboratory Reports, Vol. 6, 

 part I, 1905. 



3 Koch and Woods, Journ. of biol. Chem., 1. 



4 Thudichum, 1. c.; Koch, Zeitschr. f. physiol. Chem., 36. 



5 Compt. rend. soc. biol., 62. 



