104 PUBLIC HEALTH CHEMISTRY 



Glucose and Lcevulose are found in equal proportions in 

 all sweet fruits. It is likely that cane sugar first forms in 

 the plants, and that a ferment at once breaks it up into 

 grape sugar and fruit sugar, the mixture forming invert 

 sugar. The saccharine substance which bees collect and 

 form into honey is a mixture of these two sugars, forming 

 " invert sugar," and hence pure honey is laevo-rotatory. 



Glucose, or dextrose, or grape sugar, or blood sugar, 

 reduces Fehling's solution, ferments with .yeast, is dextro- 

 rotatory (+ 52-7), and forms six-sided crystals. 



Lcevulose, or fructose, or fruit sugar, closely resembles 

 glucose, but rotates polarized light to the left ( 95-5). 



Lactose, or sugar of milk, occurs in the milk of mammals. 

 It crystallizes with one molecule of water in rhombic 

 prisms, has a faintly sweet taste, is sparingly soluble in 

 water (i in 6 of cold and I in 2-5 of hot) and is insoluble in 

 alcohol. It reduces Fehling's solution, ferments readily 

 with lactic ferment, but not with yeast (or very slowly). 

 With dilute acids it yields galactose and dextrose. Lactose 

 is dextro-rotatory (-f 52-7) for A (i . 



Galactose is got from lactose by heating with dilute 

 sulphuric acid. It reduces Fehling, ferments with yeast, 

 and is dextro-rotatory (-f 83-3 for A,). 



Maltose is a variety of sugar formed together with 

 dextrin by the action of malt diastase upon starch. It 

 can also be produced by the action of dilute sulphuric acid 

 on starch. It ferments with yeast, reduces Fehling, is 

 soluble in alcohol, is dextro-rotatory, and crystallizes in 

 white needles + i molecule H 2 O. In the sugaring of 

 starch by diastase at 60 C, two-thirds maltose and one- 

 third of dextrin are produced thus : 



36 6 H j O 5 -f- H 2 O = C x 2 H 2 2 O ! ! + C 6 H j O 5 

 Starch Maltose Dextrin 



Starch, or amylum, is found in the cells of many plants 

 in the form of granules of vajying size (0-002 m.m. to 

 0-185 mm.). These are insoluble in cold water and in 

 alcohol. When heated with water the granules swell up 

 at 50 C., burst, partially dissolve, and form starch paste, 

 which turns the plane of polarization to the right. The 

 soluble portion is called granulose ; the insoluble, starch 



