186 BENZOIC ACID. 



plants, in this case theobromin and caffeine, may be similarly regarded as excretionary 

 products and are hence found collected in those parts of the plant which are more 

 immediately or ultimately cast off, viz. the leaves, seeds and bark. The facts 

 already stated render the consumption of theobromin and caffeine in some form or 

 other by practically the whole human race less surprising than it might at first 

 sight appear. Their universal use also indicates that they supply some distinct 

 want of the economy which cannot as yet be explained purely with reference to 

 their relationship to the nitrogenous extractives of animal tissues, but rather to the 

 physiological effect their ingestion produces. In moderate doses they exert an 

 agreeable stimulating action whereby the sensations of fatigue and drowsiness are 

 removed, the body being thus enabled to exert itself with less sense of effort and less 

 initial stimulus, and the mind is more active, clear-sighted and resistent to the 

 depressing effects of unpleasant influences. There is no evidence, as was at one 

 time assumed, that they act in any way by reducing the activity of nitrogenous 

 metabolism 1 . In the case of cocoa and chocolate we have to deal not merely with 

 the stimulating effects of the theobromin they contain, but also with the fact that 

 they are of extreme nutrient value owing to the large amount of fats (50 p.c.), 

 proteids (12 p.c.), and carbohydrates which enter into their composition. The 

 comparative physiological action of xanthin, theobromin, caffeine, and some of 

 their derivatives have recently been studied by Filehne 2 . 



THE AROMATIC SERIES. 



1. Benzole acid. C 6 H 5 . COOH. 



This is not found as a normal constituent of the body. When 

 it occurs in (chiefly herbivorous) urine its presence is usually due to a 

 fermentative decomposition of hippuric acid whereby benzoic acid and 

 glycin (glycocoll) are formed. 



C 6 H 5 . CO . NH . CH 2 . COOH . + H 2 O 



- C 6 H 5 . COOH . + CH 2 (NH 2 ) . COOH. 



The acid is usually prepared by the above decomposition of hippuric 

 acid which is readily effected by a short boiling with mineral acids 

 or, less readily, with caustic alkalis. It is also obtained by the dry 

 distillation of gum-benzoin from which the acid separates by sublima- 

 tion. The sublimed acid generally crystallises in fine needles which are 

 light and glistening. It is soluble in about 200 parts of cold or 25 of 

 boiling water and very soluble in alcohol, ether and petroleum-ether 3 , 

 in which latter hippuric acid is insoluble. When precipitated from 



1 Voit, Unters. iib. d. Einfi. d. Kochsalzes, d. Kaffees u. s. ID. Miinchen. 1860. 



2 Arch. /. Physiol. Jalirg. 1886, S. 72. See also Kobert, Arch. f. exp. Path. u. 

 Pharm. Bd. xv. (1882), S. 22, and cf. Kossbach, Pfliiger's Arch. Bd. xxvii. (1882), 

 S. 372. 



3 Petroleum-ether consists ordinarily of a mixture of the more volatile hydro- 

 carbons obtained by distillation during the fractionating of crude petroleum and 

 boils up to about 120. The most volatile petroleum-ether boils up to about 80. 



