FE. A. Csonka 7 407 
(95 per cent) and 4 gem. of stick potassium hydroxide are added. The 
flask is immersed in a boiling water bath and its contents are boiled 
under a reflux condenser for 1 hour, it is then cooled, and 20 cc. of 20 per 
cent HCl are added in small portions to free the fatty acids, cooling the 
flask after each addition of the acid. The flask is filled to the constriction 
with distilled water, 50 cc. of ether are added, the flask is closed with the 
stopper, and shaken in a rotary manner for a few minutés. After the 
ether layer has separated it is blown by pressure intoga separating funnel 
(250 ce.). The ether extraction is repeated twice Wh 50 cc. portions, 
collecting the portions in the separating funnel. After each extraction 
the ether layer is brought to the constriction by adding a little distilled 
water. The combined ether extract in the separating funnel is washed 
with several portions of water until the wash water is neutral. The crude 
ether extract, being free from hydrochloric acid as well as lower fatty 
acids, is transferred into an Erlenmeyer flask (200 cc.), a glass bead added, 
and the ether distilled off. The flask containing the residue is placed in 
the water bath for a few minutes, then in a vacuum desiccator over night 
to free the residue from moisture. 25 cc. of light, boiling petroleum ether 
are added, the flask is rotated at frequent intervals, and the solution 
filtered through a thick plug of fat-free cotton. Wash the flask and filter 
well with petroleum ether (8 times with 10 cc. portions) and collect the fil- 
trate which is perfectly clear and colorless in an Erlenmeyer flask. Bring 
the petroleum ether solution to boiling in a water bath and titrate it im- 
mediately with 0.04 nN alcoholic KOH using phenolphthalein as an indica- 
tor; each ce. of 0.04 n KOH is equal to 10.97 mg. of SR acids. For 
further details see the original article.!! 
DISCUSSION. 
The unsaturated fatty acids are of exogenous or endogenous 
origin, the latter being derived by synthesis from either carbo- 
hydrate or protein. A third source is by the desaturation of food 
fat and depot fat, which is mobilized for transport. Leathes" 
believes that desaturationis the réle of the liver in fat metabolism, 
so we may consider that unsaturated fatty acids occur in normal 
metabolism. 
As Table I shows, the blood of normal individuals contains an 
average of 0.143 gm. of unsaturated fatty acids per 100 cc. with 
an average iodine number of 87.5. 48 per cent of the total fatty 
acids are unsaturated. The iodine number of unsaturated fatty 
acids varies from 76 to 105 in normal human blood, thus indi- 
16 Leathes, J. B., Ergebn. Physiol., 1909, viii, 356. 
