PAT METABOLISM 



689 



of it Bomewhat more complex structure namely, the phospholipid. As 

 their name indicates, these consist chemically of phosphoric acid combined 

 with neutral Cat and with a nitrogenous base, cholin. The beat known of 

 the phospholipid is lecithin, which Is w idely distributed in the animal body 

 (presenl in blood and bile as well as in all cells . Other phospholipid 

 present in nervous tissue are cephalin, cuorin and sphingomyelin. Tl 

 are various lecithins distinguished from one another by the fatty-acid 

 radicles which they contain. Distearyl-lecithin, for example, has the 



formula: 



CH t -0-OC(CH 1 ) l ,-CH 



C|[ -O-OC CH . CH 

 teai ic acid I 

 cir.-o o 



\ / 



(glycerol) P 



/ \ 

 OK OCH, CH, N CH 



(phosphoi i>' 



aci.l) OH 



(cholini 



This complex molecule can readily be split up by hydrolysis (warming 

 with baryta water) into: 



glycero-phosphoric acid, ('IT. -oil 



I " 

 ('II - oil 



oir -o o 

 \ / 



P ; choline, N 



/ \ 



on oh 



C ll/'il 

 i mi w ethyl anunoninm 



oil 



hydroxide) ; and fatty acida. 



With hydrochloric aci.l, choline tonus a salt which readily forms ;i 



double salt with platinic chloride Since this double salt forms chai 



teristic crystals, it is used to identify ami separate lecithins. For quan- 

 titative purposes, however, it is more suitable to determine lecithin in- 

 directly by the amount of phosphoric acid present in an ethereal 

 tract of the organ or tU^im. 



Evidence is constantly accumulating to show that lecithin is an I 

 tremely important constituent of cells; indeed, it srcnis to he the h • 

 mediate staire in the utilization of neutral fats hy protoplasm. Its p] 



phorus also probably Berves as the source of this element for the con- 

 struction of nucleic acid i sec pa-_ r '- 637 In nervous t - t is oft 

 associated with carbohydrate molecules (galactose . forming the sul»- 

 stance known as cerebrin. It may therefore have some role to play in 

 carbohvdrate metabolism. Some workers also attribute to lecithin an 



