976 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Monobasic Acids The Fatty Acids (formula, C n H 2n O 2 ). 



Formic acid, H COOH. Capric acid, C 9 H 19 COOH. 



Acetic acid, CH 3 COOH. Laurie acid, C U H 23 COOH. 



Propionic acid, C 2 H 5 COOH. Myristic acid, C 13 H 27 COOH. 



Butyric acid, C 3 H T COOH. Palmitic acid, C 15 H 31 COOH. 



Valerianic acid, C 4 H 9 COOH. Stearic acid, C 17 H, 5 COOH. 



Caproic acid, C 5 H n COOH. Arachidic acid, C 19 H 39 COOH. 



(Enanthylic acid, C 6 H 13 COOH. Cerotic acid, C 26 H 53 COOH. 



Caprylic acid, C 7 H 15 COOH. Melissic acid, C 29 H 59 COOH. 



These are organic compounds of acid reaction in which one atom of hydrogen is replace- 

 able by a metal or an organic radical. Combined with glycerin the higher members of the 

 series (from C 4 up) form the neutral fats of the organization. By distillation of a fatty 

 acid with alkaline hydrate, a hydrocarbon is obtained containing one carbon atom less than 



the acid used. 



CH 3 COONa 4- NaOH = CH 4 + Na.COg. 



Preparation. (a) Through oxidation of alcohols or of aldehydes, 



C 2 H 5 OH + 2 = CH 3 COOH + H 2 0. 



(6) Through the action of carbon dioxide on the sodium compound of alcohol radicals, 

 CH 3 Na + C0 2 = CH 3 COONa. 



COMPOUNDS OF METHYL. 



Methane, or Marsh-gas, CH 4 . This gas is produced by intestinal putre- 

 faction, and is the only hydrocarbon found in the body. It is formed in largest 

 quantities from the fermentation of cellulose, which takes place, according to 

 Hoppe-Seyler, thus : 



C 6 H 10 5 +H 2 0-C 6 H 12 6 . 

 C 6 H U 6 - 3CH 4 + 3C0 2 . 



Tappeiner l finds that less CH 4 than CO 2 is produced in cellulose fermenta- 

 tion in the intestine, and that the lower fatty acids (acetic to valerianic) are 

 also formed. This putrefaction is especially great in the caecum of herbivora. 

 Methane is also a product of putrefaction of proteid (but not of casein, since 

 it is not present when milk is fed). Through the putrefaction of cholin, a 

 decomposition product of lecithin, methane is likewise evolved in small 

 quantity. 2 Further, methane may be produced from the putrefaction of metal- 

 lic acetates : 



CaC 4 H 6 4 + 2H 2 = CaCO 3 + CO 2 + H 2 O + 2CH 4 . 

 Properties. A colorless, odorless gas which burns with a dull flame. It is 

 absorbed by the blood, and in the herbivora is given off by the lungs often in 

 larger quantity than from the rectum. 3 In man only little is produced. Methane 

 is not oxidized in the body, and is harmless when respired, even when 10 or 20 

 per cent, in volume is present. 4 



1 Zeitschrift fur Biologie, 1884, Bd. 20, p. 84. 



2 Hasebroek : Zeitschrift fur physiologische Chemie, 1888, Bd. 12, p. 148. 



3 B. Tacke : Quoted by Bunge, Physiologische Chemie, 3d ed., 1894, p. 284. 



* Paul Bert : Comptes rendus de la Societe de Biologic, 1885, p. 523. Abstract in Maly's 

 Jahresbericht uber Thierchemie, 1886, Bd. 16, p. 364. 



