BIOLOGICAL CHEMISTRY 



pounds of galactose with fatty acids and with the nitrogenous 

 base sphingosine. 



Instead of three molecules of fatty acid uniting with one 

 molecule of glycerine, there are compounds in which two 

 molecules of fatty acid unite with glycerine and the third 

 molecule of fatty acid is replaced by phosphoric acid. Attached 

 to the phosphoric acid is a nitrogenous base : in lecithin the 

 base is cholin. 



CH 2 O OCC 17 H 3{ 

 CHO OCC 17 H 35 



[Palmityl groups. 



CH 2 P=O 



A 



OH OC 2 H 4 



Phosphoric group. 



X 



CH, 



CH 3 Cholin 

 HO' v CH 3 

 Lecithin. 



These phosphorised fats are probably essential for living 

 cells as they are found in all cells. They are classified 

 according to the relative number of atoms of nitrogen and 

 phosphorus in their molecules. 



TABLE II 



Table to show the main characters by which various natural 

 fats are distinguished from each other. 



The first two are expressed as the amount of potassium hydroxide 

 in milligrams necessary to neutralise the fatty acid in one gram of fat. 



The third is expressed as the number of cubic centimetres of O'lN 

 alkali required for the volatile fatty acids from five gram of fat. 



The last is expressed as the amount of iodine in grams absorbed by 

 100 grams of fat. 



