CHEMICAL BASIS OF THE ANIMAL BODY. 105 



possible to obtain the crystals from fluids which contain only 0*5 grm. 

 per litre. 



An important property of dextrose is its power of undergoing 

 fermentations. Of these the principal are: (1) Alcoholic. This is 

 produced in aqueous solutions of dextrose, under the influence of 

 yeast. The decomposition is the following : C 6 H 12 O 6 = 2C 2 H 6 + 2CO 2 , 

 yielding (ethyl) alcohol and carbonic anhydride. Higher alcohols of 

 the fatty series are found in traces, as also are glycerin, succinic acid 

 and probably many other bodies. The fermentation is most active at 

 about 25C. Below 5C. or above 45C. it almost entirely ceases. If 

 the saccharine solution contains more than 15 per cent, of sugar it will 

 not all be decomposed, as excess of alcohol stops the reaction. (2) 

 Lactic. This is best known as occurring in milk when it turns sour 

 owing to the conversion of lactose into lactic acid. But dextrose and 

 other sugars may also be converted into lactic acid (C 6 H 12 O 6 = 2 C 3 H 6 O 3 ), 

 the conversion being ordinarily due to the presence of some specific 

 micro-organism 1 which is specially active in presence of decomposing 

 nitrogenous material such as decaying cheese 2 . A similar change is 

 rapidly produced when dextrose is mixed with finely divided gastric 

 mucous membrane 3 . There is also some evidence of the existence of 

 an unorganised ferment (enzyme) in the mucous membrane of the 

 stomach which can convert lactose and dextrose (?) into lactic acid 4 . 

 On prolonged standing the lactic fermentation is apt to pass into (3) 

 Butyric. This results from the appearance and action of another 

 specific organised ferment on the first formed lactic acid, the change 

 being accompanied by the evolution of hydrogen and carbonic an- 

 hydride 



2C 3 H 6 3 = C 3 H 7 . COOH . + 2C0 2 + 2H 2 . 



Lactic and butyric fermentations are most active at 35 and 40 

 respectively ; they probably occur constantly in the alimentary canal 

 with a carbohydrate diet and may in some cases be remarkably pre- 

 dominant. The hydrogen evolved during butyric fermentation probably 

 plays some important part in the production of the fcecal and urinary 

 pigments from those of bile (see below). 



Dextrose is the sugar which is characteristically formed by the action of boiling 

 dilute mineral acids on sugars of the cane-sugar group, and on starch and dextrin. 

 When it is dissolved in concentrated sulphuric acid it is said to be partly recon- 



1 Lister, Path. Soc. Trans. 1873, p. 425. Quart. Jl. Micros. Sci. Vol. xvm. (1878), 

 p. 177. Marpmann, Centralb. f. allg. Gesundheitspfl. Erganzungshft. n. (1886), 

 S. 117. Meyer, Inaug.-Diss. Dorpat, 1880. Abst. in Maly's Bericht. 1881, S. 468. 



2 Bensch, Preparation of lactic acid. Liebig's Ann. Bd. LXI. (1847), S. 174. 



3 Maly, Liebig's Ann. Bd. CLXXIII. (1874), S. 227. 



4 Hammarsten (Swedish). See Abst. in Maly's Ber. Bd. n. (1872), S. 118. 



