CHAPTER VI 

 FATS AND LIPOIDS 



SECTION I. 



Neutral Fats and Fatty Acids. Fats occur widely distributed in 

 the plant and animal kingdom. In the former they occur in seeds, 

 roots, and fruits; in the latter in varying quantities in all tissues, but. 

 particularly in the adipose tissue, bone marrow, and milk. Neutral 

 fats are compounds of the fatty acids with the triatomic alcohol, 

 glycerine. They are generally yellowish in colour or colourless, and 

 when pure have neither odour nor smell. They have the general 

 formula : 



CH, CO R 



H CO R 

 CO R 



where R, the fatty acid radical, usually stands for palmitic, stearic, 

 or oleic acid. Of these, palmitic and stearic are saturated acids, and 

 have the general formula CnH^^COOH, n being 17 in stearic acid, 

 C 17 H 35 COOH, and 15 in palmitic acid, C 15 H 33 COOH. Oleic acid, 

 C 17 H 33 COOH, is unsaturated, and therefore possesses the power of 

 decolorizing dilute bromine-water and of combining with iodine. 

 This latter property is used to determine the amount of olein present in 

 the ordinary fats, which are mixtures of varying proportions of olein, 

 stearin, and palmitin. The melting-point of fat also varies according 

 to the relative amounts of these fats present. Olein is fluid at ordinary 

 temperature, melting at -5 C.; whereas palmitin melts at 45 C., 

 and stearin at about 56 C. The fluid nature of fat at body tempera- 

 ture is therefore due to the amount of olein which it contains. Butyrin 

 occurs in the fat of milk. 



When a liquid fat is shaken with soap, mucilage, or egg albumin, 

 it becomes finely divided, or " emulsified." Rancid fat emulsifies on 

 addition of alkali far more easily than neutral fat, because soap is 

 formed from the alkali, free fatty acid being present, and the soap 

 renders emulsification easier. Hence the fact that fat is rendered 

 faintly rancid in the stomach is of importance. Emulsification is a 

 physical change; the minute subdivision hastens the chemical change 

 of fat. 



By hydrolysis of fat, glycerine and fatty acid are produced. This 

 process is known as saponification, and can be brought about by such 

 agencies as superheated steam, boiling with alkali, long-continued 



53 



