Lactose. Molecular model of the sugar D-(+)- lactose (formula: C12H22O11). The atoms are spherical and colour-coded: carbon (blue), oxygen (red) and hydrogen (white). This is a disaccharide sugar found in milk. It is made of two monosaccharide units, one of glucose and one of galactose. The D in D-(+)-lactose refers to the arrangement of atoms in the molecule. The mirror image of this would be called the L" form. The + refers to the fact that a solution of the sugar rotates the plane of polarised light clockwise. This is an important sugar in the diet, but some people are lactose intolerant, and cannot digest the sugar, causing cramps and weight- loss."