1224 LACTOSE. 



5 mgr. of dextrose, requires 6*7 mgr. of lactose, provided that 

 certain conditions as to the dilution of the solution, duration 

 of boiling, etc., are attended to. These are important for the 

 accurate volumetric estimation of lactose. The specific rota- 

 tory power of lactose is (a) n = -j- 52-3°, and is independent of 

 the concentration in solutions which contain up to o5 p.c. at 

 ordinary temperatures. Its rotatory power is thus identical 

 with that of dextrose. It is, however, readily distinguish- 

 able from dextrose by its smaller solubility in water, insolu- 

 bility in alcohol, and incapability of undergoing direct alcoholic 

 fermentation with yeast. It also does not reduce Barfoed's 

 reagent, and in this resembles maltose. When boiled with 

 dilute mineral acids it yields equal molecules of dextrose and 

 galactose (see p. 1220), and since the specific rotatory power of 

 the latter of these is high [(a) D = + 83°], this increase of rota- 

 tory (and reducing) power on treatment with acids affords a 

 further convenient means of discrimination between lactose and 

 dextrose. 



Phenyl-lactosazone. C 24 H 32 N 4 9 . 



This compound of lactose with phenyl-hydrazine is formed 

 under conditions similar to those employed for the preparation 

 of the analogous compound of dextrose. It is soluble in 80 — 90 

 parts of boiling wa^er and melts at about 200°. It crystallizes 

 readily in the form of yellow needles which, unlike the crystals 

 of phenyl-maltosazone, are usually aggregated into clusters. 



Lactose is readily capable of undergoing a direct lactic fermen- 

 tation and this occurs characteristically in souring milk. The 

 exciting cause is doubtless ordinarily an organized ferment, but 

 there is also some evidence of the existence in the alimentary canal 

 of an enzyme which can effect the same conversion. The circum- 

 stances and products of the conversion are the same as for dextrose 

 and saccharose. 



Although isolated lactose is unaffected by yeast, milk itself is 

 capable of undergoing, under the influence of certain ferments, an 

 alcoholic fermentation, and this has been employed from very early 

 times by the inhabitants of certain districts of Russia in the prepa- 

 ration of Kumys from mare's milk, and Kephir from cow's milk. 

 Of late years these fluids have attracted much attention in virtue of 

 their supposed therapeutic action in certain wasting diseases. Very 

 little is as yet known as to the real nature of the changes which 

 occur during the fermentation, but they are probably extremely com- 

 plex and due to the presence of several organized ferments. Kephir fer- 

 ment is a commercial article in Russia, obtainable at the apothecaries. 



The non-assimilability of saccharose and maltose has already 

 been referred to, and experiment has shewn that lactose is 

 similarly incapable of assimilation, for when injected into the 



