1002 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



lecithin in the body, or the physiological importance of the substance, abso- 

 lutely nothing is known. 



FAT IN THE BODY. Animal and vegetable fats consist principally of 

 a mixture of the triglycerides of palmitic, stearic, and oleic acids. In the 

 intestines the fat-splitting ferments convert a small portion of fat into glycerin 

 and fatty acid ; the fatty acid unites with alkali to form a soap, in the presence 

 of which the fat breaks up into fine globules called an emulsion ; if now the 

 fine globules and the intestinal wall be wet with bile, fat is absorbed, and may 

 be burned in the cells or deposited in the adipose tissue. 



Fat may likewise be derived from ingested carbohydrates. The chemical 

 derivation of fatty acid from carbohydrates has already been mentioned in 

 the case of formic, acetic, propionic (see p. 980), and butyric acids. The fatty 

 acids of fusel oils are likewise formed from carbohydrates in fermentation. 

 The laboratory synthesis of sugar from glycerin has been already related. 

 These reactions, however, furnish only the smallest indication of the large 

 transformation of carbohydrates into fat possible in the body. 



If geese be fed with rice in large quantity, and the excreta and air respired be ana- 

 lyzed, it may be shown that carbon is retained in large amount by the body, in amount 

 too great to be entirely due to the formation of glycogen, and must therefore have been 

 deposited in the form of fat. 1 Such fattening of geese produces the delicate pati de foie 

 gras. The principle has been established in the case of the dog as well. 2 



The formation of fat from proteid (fatty degeneration) has been established 

 with all certainty in pathological cases (see p. 957). Recollection of the fact 

 that proteid may yield 45 per cent, of sugar aids in the comprehension of this 

 problem. 



Other usually cited proofs of the formation of fat from proteid include the conversion 

 of casein into fat incident to the ripening of cheese ; and the transformation of muscle in 

 a damp locality into a cheese-like mass called adipocere, which is probably effected by 

 bacteria. 3 Adipocere contains double the original quantity of fatty acid, occurring as cal- 

 cium, and sometimes as ammonium salts. 



Experiments of C. Voit show that on feeding large quantities of proteid, not all the 

 carbonic acid is expired that belongs to the proteid destroyed as indicated by the nitrogen 

 in the urine and feces. The conclusion follows that a non-nitrogenous substance has been 

 stored in the body. Too much carbon is retained to be present only in the form of glyco- 

 gen; fat from proteid must therefore have been stored. 4 The formation of fat normally 

 from proteid has been violently combated by Pfliiger, it would seem without proper founda- 

 tion. For behavior of fat in the cell see p. 999. 



Oleic Acid, C 18 H 34 O 2 . This acid belongs to the series of fatty acids hav- 

 ing the formula C n H 2n _ 2 O 2 . Its glyceride solidifies only as low as +4 C. It is 

 the principal compound of liquid oils. Pure. stearin is solid at the body's 

 temperature, but mixed with ole'm the melting-point of the mixture is reduced 

 below the temperature of the body and its absorption is thereby rendered possi- 

 ble. The fat in the body is all in a fluid condition, due to the presence of olei'n. 



1 Voit: Abstract in Jahresbericht uber Thwrchemie, 1885, Bd, 15, p. 51. 



2 Kiibner : Zeitschrift fur Biologie, 1886, Bd. 22, p. 272. 



3 Read Lehmann: Abstract in Jahresbericht uber Thierchemie, 1889, Bd. 19, p. 516. 



* Erwin Voit : Munchener medicinische Wochenschrift, No. 26, 1892 ; abstract in Jahresbericht 

 uber Thierchemie, 1892, p. 34. 



