108 FATS 



The fatty acids which are found in the naturally occurring fats 

 belong to two series, the saturated series, represented by the general 

 formula C n H 2n 02 and the unsaturated or oleic acid series represented 

 by the general formula C n H 2n . 2 O2. In this latter series of acids two 

 of the carbon atoms are united by a double bond or unsaturated link- 

 age which enables them to react very readily with hydrogen, oxygen 

 or the halogens, the double bond being converted into a single one, 

 and the remaining valencies of the carbons saturated by combination 

 with the reacting atoms. The higher fatty acids which occur in nature 

 usually have even values of n and the chain of carbon atoms is not 

 branched. 



The lower acids, having small values of n, are formed in the secre- 

 tions of the sebaceous glands, and in butter, while the tissue-fats and 

 vegetable oils are in the main composed of fats derived from higher 

 fatty acids. Thus in sweat we find: 



Formic acid, H.COOH 

 Acetic acid, CH 3 COOH 

 Propionic acid, C 2 H 5 COOH 

 Butyric acid, CsHyCOOH 

 Isovalerianic acid, C4H 9 COOH 

 Caprylic acid, C 7 H 15 COOH 



These acids are probably secreted in combination with glycerol, but 

 if the sweat be allowed to remain in contact with the skin, the glycerides 

 are attacked by bacteria which hydrolyze them, liberating the free 

 acids, to which the characteristic odor of the "unwashed" is attribut- 

 able. The odor .of the lowest members of the series, Formic and Acetic 

 Acids, is sharp, reminiscent in the former instance of ants, in the latter 

 of vinegar. Propionic Acid has an intermediate odor, while Butyric 

 Acid has the odor of rancid butter and Valerianic Acid the most intensely 

 disagreeable odor of decomposing perspiration. The highest members 

 of the fatty-acid series are non-volatile and have only very faint odors. 



In butter the lowest member of the series is butyric acid, while 

 caproic and caprylic acids also occur together with higher fatty acids 

 particularly Palmitic and Oleic Acids. 



The majority of the tissue -fats are, however, mixtures of the glycer- 

 ides of Palmitic Acid, Ci 5 H 3 iCOOH and Stearic Acid Ci 7 H 35 COOH, of 

 the saturated series, with glycerides of Oleic Acid, Ci 7 H 33 COOH, of 

 the unsaturated series. The separation of the saturated from the 

 unsaturated acids of the higher series may be accomplished by convert- 

 ing them after hydrolysis of the fat, into the lead-salts, and extracting 

 them with ether. The lead-salts of the higher fatty acids of the satur- 

 ated series are almost insoluble in ether, while those of the unsaturated 

 series readily dissolve in this solvent. The ether extract therefore 

 contains all of the unsaturated fatty acids in combination with lead. 

 The lead may be removed by extraction of the ether with dilute hydro- 

 chloric acid, leaving the free fatty acids dissolved in the ether. 



