PHOSPHATIDES. 241 



Attention has been called in Chapter I to the importance of the phos- 

 phatides (lipoids) for the limiting layer of the cells as well as for the 

 osmotic processes 'and for the metabolism of the cells. The unsat- 

 urated, readily oxidizable phosphatides also play a possible role as oxygen 

 carriers and the phosphatides are undoubtedly of great importance as 

 constituents of the food-stuffs. There is also no doubt that they are 

 very important for development and growth. It has been found that 

 the amount of phosphatides is especially abundant in the new-born, 

 and that these latter, to a certain extent, bring into the world a store of 

 phosphatides and this store diminishes during growth. 1 



The phosphatides seem to be closely related to 'one another; they 

 influence the solubility and precipitation properties of one another, and 

 are generally precipitated as mixtures which are extremely difficult 

 to separate into individual constituents. They are also amorphous, 

 and readily oxidized, and it is easy to understand* why their preparation 

 in a pure state is so extremely difficult. Under these circumstances 

 we have no sufficient guarantee as to their chemical individuality, and 

 the description of their properties and composition must be accepted 

 with some reservation. 



The phosphatides are generally amorphous, colorless or yellowish; 

 they melt, on warming, and burn. As a rule they are insoluble in water 

 and swell up therein forming colloidal solutions, which are precipitated by 

 certain salts. The phosphatides as above stated, belong to the lipoids 

 and it is for this reason that each phosphatide is dissolved by at least one 

 of the solvents for fats (alcohol, ether, benzene, petroleum ether, etc.). 

 The lipoid group cannot be otherwise characterized. Originally we 

 included in this group, bodies similar to fat or in certain respects related 

 to the fats such as phosphatides, cholesterin and cerebrosides, but later 

 the conception has been developed and now we consider as lipoids 

 those bodies that are soluble in ether or equivalent. Under these 

 circumstances, as the diverse known and unknown bodies, such as lactic 

 acid, phenols, alkaloids and extractive bodies of various kinds may 

 belong to the lipoid group there does not seem to be any sense in speaking 

 of a special lipoid group, and especially from a chemical standpoint it 

 would be better to drop the name entirely. 



The various phosphatides shoiT a different behavior toward the 

 solvents for lipoids, namely some are soluble in ether while others 

 are insoluble therein, etc., and these differences are important for their 



1 In regard to the quantity and importance of the phosphatides (the lecithins) 

 see Siwertzow, Bioch. CentralbL, 2, 310; Glikin, Bioch. Zeitschr., 4 and 7; Nerking, 

 ibid,, 10; Stoklasa, Ber. d. d. chem. Gesellsch., 29, Wien. Sitz. Ber., 104; Zeitschr. 

 f. physiol. Chem. 25; Danilewsky, Compt. Rend., 121 and 123 and W. Koch., Zeitschr. 

 f. physiol. Chem., 37; Kyes, ibid., 41 and Berl. klin. Wochenschr., 1904. 



