30 THE LECITHINS. 



66. Show that olive-oil is not a simple fat, but a 

 mixture, by cooling it to the freezing-point either by nat- 

 ural cold or by a freezing mixture. It separates into two 

 parts: one crystalline, consisting mostly of palmitin, and 

 the other olein, which remains liquid. 



THE LECITHINS. 



The lecithins are found in nearly all animal and vege- 

 table cells. They are very abundant in the brain and 

 nerves and in the yelk of eggs. They are sometimes called 

 phosphorized fats. The formula of one of those most com- 

 mon in the animal body is.C 44 H 90 KP0 9 , and the composi- 

 tion is probably 



CH0 



It is therefore a fat where for one stearic acid radical 

 has been substituted the group 



-P0 3 OH C 2 H 4 N(CH 3 ) 3 OH. 



In others, instead of the stearic acid radical we may 

 have the oleic or palmitic radical. Like other fats, they 

 can be decomposed or saponified. They then give phos- 

 phoric acid, a fatty acid, and a base, cholin: 



HO C 2 H 4 N(CH 3 ) 3 OH. 



Lecithin is a soft, waxy substance, which swells in 

 water to a pasty mass. This, under the microscope, has the 

 form of oily drops or threads, the so-called "myelin" forms. 

 It resembles nuclein in the readiness with which it unites 



