ISO W. R. BLOOR 



may bo regarded as phosphorized fats glycerides in which one fatty acid 

 has be-on replaced by a substituted phosphoric acid. On hydrolysis they 

 yield fatty acids, giyeerepiiospliorie acid and a basic substance, which in 

 the caso of lecithin is mainly cliolin and in cephalin probably aminoethyl 

 alcohol. 



In Cnorin, a phospholipoid from heart muscle, the proportion of phos- 

 phoric acid to fatty acid is greater than in lecithin. 



Since satisfactory chemical characterization and identification of most 

 members of this group has not yet been made reference will be made to 

 only a very few. 



In general they are very active chemically, undergoing rapid changes 

 in air and light, becoming colored and rancid. They are not soluble in 

 water in the ordinary sense, but. mix with it, forming opalescent colloidal 

 suspensions. They are readily hydrolized by many reagents as well as by 

 tho lipases and esterases and even by boiling with alcohol (Erlandsen). 

 They form combinations readily with many substances, as, for example, 

 with proteins arid carbohydrates, but these combinations are unstable 

 and of inconstant composition, so that it is doubtful whether they are true 

 chemical compounds. The similarity in chemical composition indicates a 

 close relationship to the fats; the constant occurrence in quantity in living 

 active cells, the ready reactivity to oxidation, hydrolysis and combination 

 with other tissue constituents and, above all, the miscibility with the uni- 

 versal solvent, water, indicate that the phospholipoids are the intermediate 

 step through which the fats pass before being finally utilized. Tho fatty 

 acids obtained from the phospholipoids were thought by the earlier investi- 

 gators (Hoppo Seyler, etc.) to be the same as those in ordinary animal 

 fats, i. e., stearic. palmitic and oleie, but recent work, particularly that of 

 Loathes (c), 1910, Hartley (a), 1907-08, Erlandsen and Mac-Lean have 

 shown that the earlier supposition is not correct and that, if care be taken 

 to avoid oxidation, mainly unsaturated fatty acids are obtained. 



The Lecithins. The best known of the phospholipoids. They are char- 

 acterized by their insolubility in acetone a property which is made use 

 of in their separation. They are readily soluble in other fat solvents and 

 form a colloidal solution with water. Most members of this group are very 

 sensitive to chemical change, so that it is almost impossible to prepare 

 them in pure form. Tn addition to their chemical sensitiveness they pos- 

 sess, in a higher degree than most other organic compounds, the power of 

 uniting with other substances such as salts (NaCl), compounds of the 

 heavy metals as Pt and Cd, and with many organic substances such as 

 alkaloids, toxins (snake venoms), carbohydrates and proteins. These 

 combinations are not of constant, composition and are broken up by rel- 

 atively gentle treatment, e. g., boiling with neutral solvents, and it is 

 therefore a question whether they are true chemical compounds or merely 

 physical (adsorption) mixtures. This power of combination is of great 



