CH. XXVIII.] THE CARBOnYDRATES 411 



intestinal juice. It then takes up water, and is split into equal parts 

 of dextrose and laevulose. 



C 12 H 22 O 



[Cane sugar.] 



H 2 = C 6 H 12 6 + C 6 H 12 6 . 



[Cane sugar.] [Dextrose.] [Ltevulose.] 



With yeast, cane sugar is first inverted by means of a special enzyme 

 invertase secreted by the yeast cells, and then there is an alcoholic 

 fermentation of the monosaccharides so formed, which is accomplished 

 by another enzyme called zymase. 



Lactose, or Milk Sugar, occurs in milk. It is occasionally 

 found in the urine of women in the early days of lactation, or after 

 weaning. It is crystallisable, 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 i2 H 22n + H 2 = C 6 H 12 6 + C 6 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 enzymes secreted by certain micro-organisms, 

 which are somewhat similar to yeast cells. 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 12 H 22 O n + H,0 = 4C S H 6 3 . 



[Lactose.] [Lactic acid.] 



(2.) 4C 3 H 6 3 = 2C 4 H 8 2 + 4CO 9 + 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 enzymes 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 enzymes such as 

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



C 12 H 9i> O 11 + H 9 O = 2C 6 H 19 O (! . 



[Maltose.] [Dextrose.] 



