382 ORGANIC ACIDS AND ALCOHOLS. 



The neutral fats [palmitin, stearin (both solid), and olein (fluid)], the glycerides of fatty acids, 

 and of oleic acid, are triple ethers of triatomic alcohol glycerin. With the neutral fats may 

 be associated glycerin-phosphoric acid, an acid glycerin ether, formed by the union of glycerin 

 .and phosphoric acid, with the giving off of a molecule of water (C :) H 9 PO tt ) ; it is a decomposi- 

 tion-product of lecithin ( 23). 



(3) Tljc glycolic acids (acids of the lactic acid series) have the formula C n H sn - 9 0(OH) 2 . 

 They are formed by oxidation from the fatty acid series by substituting OH (hydroxyl) for one 

 atom of H of the fatty acids. Conversely, fatty acids may be obtained from the glycolic acids. 

 The following acids of this series occur in the body : 



(a) Carbonic Acid (oxy-formic acid), CO(OH)., ; in this form, however, it only makes salts. 

 Free carbonic acid or carbon dioxide is an anhydride of the same = C0 2 . 



(b) Glycolic Acid (oxy-acetic acid), C 2 H 2 0(OH) 2 , does not occur free in the body. One of its 

 compounds, glycin (glycocoll, amido-acetic acid, or gelatin-sugar), occurs as a conjugate 

 acid, viz., as glycoeholic acid in the bile ( 177, 2), and as hippuric acid in the urine ( 260). 

 Glycin exists in complex combination in the gelatin. 



(c) Lactic Acid (oxy-propionic acid), C 3 H 4 0(OH) 2 , occurs in the body in two isomeric forms 

 1. The cthylidcnc-lactic acid, which occurs in two modifications as the right rotatory 

 sarcolactic acid (paralactic), a metabolic product of muscle ; and as the ordinary optically in- 

 active product of " lactic fermentation," which occurs in gastric juice, in sour milk (sauerkraut, 

 acid cucumber), and can be obtained by fermentation from sugar ( 184). 2. The isomer, 

 ethylene-Iodic acid, occurs in the watery extract of muscles ( 293). 



(d) Leucic Acid (oxy-caproic acid), C 6 H 12 3 , does not occur as such, but only in the form of 

 one of its derivatives, leucin (amido-caproic acid), as a product of the metabolism in many tissues, 

 and is formed during pancreatic digestion ( 170, II.). Leucic acid may be prepared from 

 leucin, and glycolic acid from glycin, by the action of nitrous acid. 



(4) Acids of the Oxalic Acid or Succinic Acid Series, having the formula C n H 2n - 4 2 (0H) 2 , 

 are bi-basic acids, which are formed as completely oxidised products by the oxidation of fatty 

 acids and glycolic acid, water being removed. It is important to note their origin from sub- 

 stances rich in carbon, e.g., fats, carbohydrates, and proteids. 



(a) Oxalic Acid, C 2 2 (OH) 2 , arises from the oxidation of glycol, glycin, cellulose, sugar, 

 starch, glycerin, and many vegetable acids it occurs in the urine as calcium oxalate 

 ( 260). 



(b) Succinic Acid, C 4 H 4 2 (OH) 2 , has been found in small amount in animal solids and fluids ; 

 spleen, liver, thymus, thyroid ; in the fluids of echinococcus, hydrocephalus, and hydrocele, and 

 more abundantly in dog's urine after fatty and flesh food ; in rabbit's urine after feeding with 

 yellow turnips. It is also formed in small amount during alcoholic fermentation ( 150). 



(5) Cholalic Acid in the bile ( 177) and in the intestine ( 182). 



(6) Aromatic Acids contain the radicle of benzol. Benzoic acid ( = phenyl-formic acid) 

 occurs in urine united with glycin, as hippuric acid ( 260). 



III. Alcohols. 

 Alcohols are bodies which originate from carbohydrates, in which the radical hydroxyl (HO) 



H ) 

 is substituted for one or more atoms of H. They may be regarded as water, jV ( O, in which 



the half of the H is replaced by a CH compound. Thus, C 2 H 6 (ethyl-hydrogen) passes into 



O (ethylic alcohol). 



H 



C H ) 



(a) Chole8terin, - 6 ij* | O, is a true monatomic alcohol, and occurs in blood, yelk, brain, 



bile ( 177, 4), and generally in vegetable cells, and it is the only solid monatomic alcohol in 

 the body. 



fOH 



(b) Glycerin, C,H 5 A OH, is a triatomic alcohol. It occurs in neutral fats united with 



I OH 

 fatty acids and oleic acid; it is formed by the splitting- up of neutral fats during pancreatic 

 digestion ( 170, III.), and during the alcoholic fermentation ( 150). 



(c) Phenol ( = phenylic acid, carbolic acid, oxybenzol) ( 184, III.). 



(d) Pyrokatechin ( = dioxybenzol) ( 252). 



(e) The Sugars are closely related to the alcohols, and they may be regarded as polyatomic 

 alcohols. Their constitution is unknown. Together with a series of closely-related bodies 

 they form the great group of the carbohydrates, some of which occur in the animal body, while 

 others are widely distributed in the vegetable kingdom. 



252. THE CARBOHYDRATES. Occur in plants and animals, and received their name, 

 because in addition to C (at least 6 atoms), they contain H and O, in the proportion in which 

 these occur in water. They are all solid, chemically indifferent, and without odour. They 

 have either a sweet taste (sugars), or can be readily changed into sugars by the action of dilute 

 acids ; they rotate the ray of polarised light either to the right or left ; as far as their 



