CHEMICAL BASIS OF THE ANIMAL BODY. 1219 



tion. (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 6 = 2C 3 H 6 3 ), the conversion being 

 ordinarily due to the presence of some specific micro-organism 

 which is specially active in presence of decomposing nitro- 

 genous material such as decaying cheese. A similar change is 

 rapidly produced when dextrose is mixed with finely divided 

 gastric mucous membrane. There is also some evidence of the 

 existence of an unorganized ferment (enzyme) in the mucous 

 membrane of the stomach which can convert lactose and dex- 

 trose (?) into lactic acid. On prolonged standing the lactic 

 fermentation is apt to pass into (3) Butyric. This results 

 from the appearance and action of another specific organized 

 ferment on the first formed lactic acid, the change being accom- 

 panied by the evolution of hydrogen and carbon dioxide — 



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 re- 

 markably predominant. The hydrogen evolved during butyric 

 fermentation possibly plays some important part in the produc- 

 tion of the f cecal and urinary pigments from those of bile. 



2. Laevulose. 



C 6 H i2°6- [CH 2 .OH-CO-(CH.OH) 3 -CH 2 .OH]. 



This is the ketone corresponding to the aldehyde dextrose. 

 It is best known as occurring mixed with dextrose in many 

 fruits, also in honey, and is stated to occur occasionally in 

 urine. It is a characteristic product of the action of dilute 

 mineral acids on cane-sugar, which is hereby decomposed into 

 equal parts of dextrose and kevulose, and since, when the 

 change is complete, the original dextrorotatory power of the 

 solution has become hevorotatory, the cane-sugar is said to 

 have been 'inverted.' A similar inversion takes place in the 

 stomach and small intestine. In its general reactions ltevulose 

 behaves like dextrose, but may be at once distinguished from 

 the latter by its powerful lsevorotatory action on polarized 

 light: this varies considerably with the temperature and con- 

 centration of the solution. It yields with phenyl-hydrazine 

 an osazone identical with that derived from dextrose. It 

 forms a compound with calcium hydrate, which unlike that 

 i elded by dextrose is extremely insoluble and may thus be 

 mloyed for the separation of the two sugars. 



