LACTOSE 3 



under normal conditions is ^ lactose orj [nilk_fiugaj. Lactose is a 

 disaccharide of the empiiical formula C12H22QU and is found 

 in the milk of most mammals. Lactose is secreted in the gland 

 and is found only in the milk, though, if suckling is interrupted, 

 it may appear in the urine, from wliich is it eUminated on re- 

 moval of the lactating gland: if the gland is removed before 

 the lactation period commences it may not appear at all. The 

 fact that the blood in the mammary vein before parturition and 

 during lactation contains less dextrose than the blood of the 

 jugular vein (Kaufman and Lagne) suggests either dextrose, or 

 the constituents from which dextrose is formed, as the source 

 of lactose. 



Two forms_DLla€t(5se"^ist and are known as thejalpha and 

 beta varieties. When lactose is obtained by crystallisation 

 from ^w^ter, the alpha modification, which crystallises in the 

 rhombic form, is formed: this modification exhibits the phe- 

 nomenon of multirotation, i.e., shows a decreasing specific 

 rotation with lapse of time after solution in water. For a 

 short period of time, the length of which depends upon the 

 temperature, the solution of alpha lactose shows a specific 

 rotation of [«]/)= +84.0, but this gradually diminishes until a 

 value of +52.5 is reached, this being the specific rotation of the 

 stable variety of lactose containing one molecule of water. 

 The corresponding value of the anhydrous lactose is +55.3. 

 Anhydrous lactose, obtained by heating the hydrated carbo- 

 hydrate to 130° C, does not produce multi-rotation in aqueous 

 solutions. The beta modification, produced by rapid evapora- 

 tion of aqueous solutions of lactose in metal vessels, has a 

 specific rotation [«]/>+ 32. 7 and shows the same birotation 



. . initial rotation .. i u ^-a j.- ■ ^n 



ratio, I.e., -^ — \ — ——. — as the alpha modification, viz., 1.6. 

 final rotation 



This shows that the reaction is mono-molecular in character. 



The density of the alpha variety is 1.545 j|^ and that of a 



solution containing 10 grams per 100 c.cms., 1.0391 yf^. The 



specific rotation is [a]D = 52.5 at 20° C. and is lowered 0.075 for 



each degree rise in temperature. The refractive index ^i?^° of 



