C1I. XXV.] SUGARS .391 



weaning. It is crystallisablo, dextro-rotatory, much less soluble in 

 water than other sugars, and has only a slightly sweet taste. It 

 gives Trommer's test, but when the reducing power is tested quanti- 

 tatively by Fehling's solution it is found to be a less powerful reduc- 

 ing agent than dextrose, in the proportion of 7 to 10. 



When hydrolysed by similar agencies as those mentioned in con- 

 nection with cane sugar, it takes up water and splits into dextrose 

 and galactose. > 



C 12 H 22 O n + H 2 =: C 6 H 12 O rt + C fi H ]2 6 . 



[Lactose.] [Dextrose.] [Galactose.] 



With yeast it is first inverted, and then alcohol is formed. This, how- 

 ever, occurs slowly. 



The lactic acid fermentation which occurs when milk turns sour is 

 brought about by lactic acid micro-organisms which are somewhat 

 similar to yeast cells. Putrefactive bacteria in the intestine bring 

 about the same result. The two stages of the lactic acid fermentation 

 are represented in the following equations : 



(1.) C 19 H 92 O n + H 2 = 4C 3 H 6 (\. 



[Lactose.] [Lactic acid.] 



(2.) 4C 3 H 6 O 3 = 2C 4 H 8 O 2 + 4CO 2 + 4H 2 . 



[Lactic acid.] [Butyric acid.] 



Maltose is the chief end product of the action of malt diastase on 

 starch, and is also formed as an intermediate product in the action of 

 dilute sulphuric acid on the same substance. It is the chief sugar 

 formed from starch by the diastatic ferments contained in the saliva 

 and pancreatic juice. It can be obtained in the form of acicular 

 crystals, and is strongly dextro-rotatory. It gives Trommer's test ; 

 but its reducing power, as measured by Fehling's solution, is one- third 

 less than that of dextrose. With yeast it yields alcohol. 



By prolonged boiling with water, or, more readily, by boiling with 

 a dilute mineral acid, or by means of an inverting ferment, such as 

 occurs in the intestinal juice, it is converted into dextrose. 



C 12 H 20 O n + H 2 = 2C 6 H 19 6 . 



[Maltose.] [Dextrose.] 



Phenyl Hydrazine Test. The three important reducing sugars 

 with which we have to deal in physiology are dextrose, lactose, and 

 maltose. They may be distinguished by their relative reducing 

 powers on Fehling's solution, or by the characters of their osazones. 

 The osazone is formed in each case by adding phenyl hydrazine hydro- 

 chloride, and sodium acetate, and boiling the mixture for half an hour. 

 In each case the osazone is deposited in the form of bright canary- 

 coloured, needle -like crystals, usually in bunches, which differ in their 

 crystalline form, melting-point, and solubilities. Cane sugar does not 

 yield an osazone, 



