

ELEMENTARY PHYSIOLOGICAL CHEMISTRY 183 



globules remain suspended, and an emulsion results. This is more 

 permanent if some suspending medium such as mucilage be added. 



EXPERIMENT V. In one test tube (a) place some soap solution ; in 

 another (b) some water. To each add some neutral olive oil and 

 shake. Allow to stand, and note that a remains emulsified, b does not. 



EXPERIMENT VI. Place some rancid oil (i.e. containing free fatty 

 acid) in a test tube add some weak KOH solution and shake; an 

 emulsion forms, soap being formed by the alkali combining with the 

 fatty acid. 



EXPERIMENT VII. Divide the emulsion produced in Experiment 

 VI. into two; to one of these add a little mucilage or egg-albumin 

 and shake, and note that the emulsion * stands ' much longer than that 

 to which no suspending medium has been added. 



Lecithin. This body is found chiefly in nervous matter, in the 

 stroma of red blood corpuscles, and in bile. Chemically it consists 

 of a molecule of glycerine, two of the hydroxyl groups of which are 

 combined with fatty acid, and the third with phosphoric acid, which 

 on the other hand has attached to it a nitrogen containing body 

 called cholin. 



2 - ir35 ] 



v 



-OOCC 17 H 3 J 

 CH-0-P=0 



Thus: CH 2 -OOCC ir H 



vStearic acid. 



CH - 



2 



Glycerine. \Q - N - CH 2 - CH 2 OH. 



Phosphoric Cholin. 

 acid. 



This cholin is a poisonous alkaloid, and is broken off from lecithin 

 during digestion, but is at once destroyed by the intestinal bacteria, 

 the substances thus produced being methane, carbonic acid, and 

 ammonia. 



Lecithin has all the solubilities of fat, but is identified by its ash 

 containing phosphorus, and by the presence of cholin (see Advanced 

 Course, p. 434). Since it contains glycerine it will give the acrolein 

 reaction. 



Cholesterin. This is found in most tissues, but especially in the 

 bile and red blood-corpuscles. It is chemically of the nature of a 

 monatomic alcohol containing twenty-six carbon atoms. Except that 

 it is soluble in the same solvents as are fats it does not give any of 

 the above reactions. It has, however, certain characteristic reactions 

 of its own, and these are as follows : 



EXPERIMENT VIII. Some cholesterin crystals are given round 



