FATS. 



463 



Formic acid, CH 2 O 2 , 

 Acetic acid, C 2 H 4 O 2 



i. 



2. , 242 , 



3. Propionic acid, C 3 H 6 O 2 , 



4. Butyric acids, C 4 H 8 O 2 , 

 5. 



6. 

 7. 

 8. 

 9. 

 10. 



Valerianic acid, C 5 Hi O 2 , 

 Caproic acids, C 6 H 12 O 2 , 

 Enanthylic acids, C 7 H 14 O 2 , 

 Caprylic acids, C 8 H 16 O 2 , 

 Pelargonic acid, C 9 H 18 O 2 , 

 Capric acid, C ]0 H 20 O 2 , 

 Undecylic acids, CnH^O^ 



12. Laurostearic acid, C 12 H 24 O fl , 



A j J. \SL \>CL*~L\^^y iiv* CU^XVl0f V^iciJ. 



1 6. Palmitic acids, C, 6 H 32 O 2 , 



17. Margaric acids, C 17 H 34 O 2 , 



1 8. Stearic acids, C 18 H 36 O 2 , 



19. Arachinic acid, C^H^Oj, 



20. Hyenic acid, C 25 H 50 O 2 , 



21. Cerotic acid, C 27 H 34 O 2 , 



22. Melissic acid, C 30 H 60 O 2 , etc. 



The acids form an homologous series according to the formula C n H 2n - 1 O(pH). 

 With each additional CH 2 the boiling-point is raised 19. The acids containing a 

 larger amount of carbon are consistent and do not volatilize; those containing a 

 lesser amount of carbon (to 10 inclusive) are oleaginous and volatile, with a 

 pungent acid taste and a rancid odor. The earlier may be produced from the 

 later in the series by oxidation, CH 2 disappearing, with the formation of CO 2 

 and H 2 O: for example, butyric acid results from propionic acid. Human and 

 animal fat contain 16 and 18, in smaller amount and inconstantly 14, 12, 6, 8, 

 10, 4. Some are contained in the sweat and in the milk. Many develop from 

 albumin and gelatin in the process of putrefaction. The majority, with the ex- 

 ception of those from 19 to 22, are present in the contents of the large intestine. 



2. In addition, glycerin combines with the monobasic oleic acids, which like- 

 wise form a series and stand in an intimate relation to the fatty acids. Their 

 general formula is C n H 2n - 3 O(OH) ; they all thus possess 2H less than the cor- 

 responding members of the fatty-acid series. By suitable procedures the cor- 

 responding fatty acids can be obtained from the oleic acids, and conversely 

 oleic acids develop from the corresponding fatty acids. Oleic acid (elaic acid) , 

 C }8 H 34 O 2 , is the only member found in the organism; combined with glycerin it 

 yields fluid olein. The fat in the new-born contains more glycerids of palmitic 

 and stearic acids than that of the adult, which contains more glycerids of oleic 

 acid. In addition, oleic acid occurs in combination with alkalies (in soaps), and, 

 like a number of fatty acids, in the lecithins. Lecithin is considered as a glycero- 

 phosphate of neurin, in which two atoms of H in the radicle of glycero-phosphoric 

 acid are replaced by two atoms of stearic, palmitic, or oleic acid. If barium 

 hydrate is added to lecithins, insoluble barium stearate or oleate or palmitate 

 + oleate is produced, together with neurin in solution and barium glycero-phos- 

 phate. There appear to be different lecithins, of which those combined with the 

 stearic-acid and that with the palmitic-acid + oleic-acid radicle are the most 

 frequent. Lecithin is present in the blood-corpuscles, in larger amount in the 

 semen, in the yolk of birds, in the nervous tissue, in traces in all animal cells. 

 Neurin also is a constant constituent of bacteria and of the seeds of vetch and peas. 



The neutral fats, the glycerids of the fatty acids and of oleic acid, are triple 

 ethers of the triatomic alcohol, glycerin. Fat in the ordinary sense of the word 

 consists of palmitin (with a melting-point of 62), stearin (71.5), olein (o). 

 Related to the neutral fats is glycero-phosphoric acid, an acid glycerin-ether, 

 resulting from the combination of glycerin with phosphoric acid, with the giving 

 off of i molecule of water C 3 H fl PO 6 ; it is a product of the decomposition of 

 lecithin. Spermaceti (cetaceum) , obtained from the cranial cavity of certain 

 whales, contains principally palmitic-acid cetyl-ether. 



3. The glycolic acids, acids of the lactic-acid series, are constructed according 

 to the formula C n H n - 2 O(OH) 2 . They result from the fatty acids by oxidation, 

 if i atom of H in the fatty acids is replaced by OH (hydroxyl). Conversely also 

 fatty acids can be obtained from the glycolic acids. Those fatty acids that (from 

 propionic acid downward) contain more than 2 atoms of C may form various 

 isomeric glycolic acids, in accordance with the C-atom in which the other hydroxl- 

 group enters. There occur in the body 



(a) Carbonic acid, hydrooxyformic acid, CO(OH) 2 , in this form, however, 

 forming only salts. Free carbonic acid is the anhydrid, namely CO 2 . 



(6) Glycolic acid, oxyacetic acid, C 2 H 2 O(OH) 2 , does not occur in the body 

 in the free state. A combination of this, glycin glycocol, amido-acetic acid, 

 gelatin-sugaroccurs as a conjugate acid, namely as glycocholic acid in the bile 

 and as hippuric acid in the urine. Glycin exists in gelatin in complex combination. 



(c) Lactic acid, oxypropionic acid, C 3 H 4 O(OH) 2 , is contained in the body 

 in two isomeric forms: (i) Ethylidene lactic acid, which occurs in two modifica- 



