Galactose, a sugar containing six atoms of carbon in the molecule. It originally received the name lactose, but this is now applied to a totally different compound, milk sugar, from which galactose itself, together with the isomeric dextrose, may be prepared by boiling for some hours with a dilute acid. It has the same composition as dextrose, which it further resembles in its action on polarised light, being dextro-rotatory, in fermenting under the influence of yeast, and in reducing Fehling's solution (q.v.). It forms small prismatic crystals, which melt at 166°, and which are soluble in water, though not as readily as dextrose. It yields by oxidation two acids - (1) galactonic acid, and (2) mucic acid, while by reduction it gives rise to a body of the nature of an alcohol, dulcitol (q.v.). It is estimated quantitatively in the same manner as dextrose.