LIPINS 51 



of digitonin in 95 per cent alcohol until no further precipitate 

 is formed ; a little chloroform is then added to prevent the 

 separation of any excess of digitonin and the whole is allowed 

 to stand for some hours while the precipitate of the sterol 

 digitonide settles down ; the precipitate is then filtered off 

 on a Gooch crucible, washed with chloroform and finally 

 with ether, dried for 10 minutes in a steam oven, and weighed. 

 The weight multiplied by the factor 0-2431 gives the weight 

 of sterol. 



LIPINS. 



The term lipin is applied to a group of glycerol esters which 

 in their physical and chemical properties are closely allied to 

 the fats. The nomenclature of the group has in the past 

 given rise to much confusion, the term lipoid (from the Greek 

 word AtTTos- = fat) having been used somewhat loosely to in- 

 clude a heterogeneous group of substances which were all 

 soluble in the ordinary fat solvents, but were not necessarily 

 esters of glycerol. 



Like the fats, the lipins are esters of glycerol with saturated 

 fatty acids and with unsaturated acids of the oleic and other 

 series, but they differ from the fats in containing in addition 

 the elements nitrogen and phosphorus, or nitrogen only, as is 

 exemplified by the formula here given for lecithin, one of the 

 best-known representatives of the group : — ■ 



CHj . O . COC17H35 (Stearyl) 



:H . O . COC„H33 (Oleyl) 



P(OH) . O . CH2CH,N(CH3)<,OH 



II 

 O 



CH„ . O . 



As already stated the phospho-lipins in general resemble the 

 fats in being soluble in the same solvents such as ether, petrol, 

 benzene, etc. ; they are, however, generally more soluble in 

 alcohol than the fats, but on the other hand they are insoluble 

 in cold acetone though frequently soluble in hot acetone ; 

 the cerebrosides are practically insoluble in ether. 



The fact that lipins are themselves soluble in fats and are 

 usually found in close association with true fats in plant and 



