THE COMPONENTS OF PLANTS AND ANIMALS 23 



The molecular structure of the lecithins is illustrated by the fol- 

 lowing formula for distearyl lecithin : 



CH 2 -0-C 18 H3 6 O 



I 



CH -O-Ci 8 H 36 O 



I 

 CH 2 -0 



HO-PO 



/ 

 CH 2 -0 



I 



CH 2 -N = (CH 3 ) 3 



OH 



The lecithins resemble fats in their general properties. They 

 are soluble in ether but, unlike the fats, readily form permanent 

 emulsions or colloidal solutions with water. On hydrolysis, 

 they yield fatty acids, glycero-phosphoric acid and cholin. 

 They are found widely distributed both in animals and plants 

 and appear to be essential constituents of protoplasm. 



38. Other phosphatids. A variety of other lipoids of the type of 

 the lecithins, but differing in both the fatty acid and the nitrogenous 

 base which they contain and likewise in the ratio of phosphorus to 

 nitrogen, have been described, but the chemistry of this group is still 

 in a very unsatisfactory state. The various phosphatid preparations 

 obtained from vegetable materials, especially seeds, by E. Schulze 

 and his associates and designated as lecithins are held by other 

 authors to be such only in a generic sense and in some cases are re- 

 garded as more analogous to the cerebrosids or galactolipins of the 

 succeeding paragraph. 



Cerebrosids or Galactolipins 



39. This group of substances, found especially in the brain and in 

 nerve tissue in general, belongs chemically to the lipoids, since its 

 members yield fatty acids on hydrolysis. The other products of 

 hydrolysis are galactose and nitrogenous substances but no phosphoric 

 acid, but the constitution of these compounds is still unknown. 



