CHEMICAL BASIS OF THE ANIMAL BODY. 1227 



Butyric acid. C 3 H 7 . COOH. 



There are two possible isomeric acids of the general formula 

 C 3 H 7 . COOH, the normal or primary, CH 3 . CH 2 . CH 2 . COOH 

 and iso- or secondary, CH(CH 3 ) 2 . COOH. 



Normal butyric acid. An oily colourless liquid, with an 

 odour of rancid butter, soluble in water, alcohol, and ether, 

 boiling at 162 C. 



Found in sweat, the contents of the large intestine, faeces, 

 and in urine. It occurs in traces in many other fluids, and is 

 plentifully obtained when diabetic urine is mixed with pow- 

 dered chalk and kept at a temperature of 35 C. It exists, in 

 union with glycerin as a neutral fat, in small quantities in milk, 

 and gives the characteristic odour to butter which has become 

 rancid. 



It is the principal product of the second stage of lactic fer- 

 mentation (see p. 1219), and is ordinarily prepared from this 

 source. 



Isobutyric acid. Occurs in faeces and among the putrefac- 

 tive products from proteids, also in certain fruits such as the 

 banana. 



Valeric or Valerianic acid. C 4 H 9 . COOH. 



Four isomeric forms of this acid exist. Of these the one 

 here described is the isoprimary CH(CH 3 ) 2 CH 2 .COOH. 

 (Isopropyl-acetic acid.) 



An oily liquid, of burning taste and penetrating odour as of 

 decaying cheese; soluble in 30 parts of water at 12 C., readily 

 soluble in alcohol and in ether. Boils at 175 C. 



It is found in the solid excrements, and is formed readily 

 by the decomposition, through putrefaction, of impure leucine, 

 ammonia being at the same time evolved ; hence its occurrence 

 in urine when that fluid contains leucine, as in cases of acute 

 atrophy of the liver. 



Caproic acid. C 5 H n . COOH. 

 Caprylic acid. C 7 H 15 . COOH. 

 Capric (Rutic) acid. C 9 H 19 . COOH. 



These three occur together (as fats) in butter, and are con- 

 tained in varying proportions in the faeces from a meat diet 

 and the first two in sweat. The first is an oily fluid, slightly 

 soluble in water, the others are solids and scarcely soluble in 

 water; they are soluble in all proportions in alcohol and in 

 ether. They may be prepared from butter, and separated by 

 the varying solubilities of their barium salts. 



