240 A. I. I1IXGER AND EMIL J. BALTMANX 



urine of pregnant and lactating women. Human milk contains 5 to 7 

 per cent lactose, occasionally more, while the milk of other animals con- 

 tains somewhat less. 



Lactose is readily prepared from milk by coagulation of the casein 

 \virh the enzyme rennet, and the clear liquid or whey which separates from 

 thr precipitated protein is concentrated under diminished pressure to a 

 svrup, from which crude lactose-crystallizes. It is purified hy recrystalliza- 

 tion from water. 



Erdmann (1855) obtained lactose in two crystalline forms, one of 

 which had a specific rotation of 4- 90 and the other of + 35, each show- 

 ing a motarotation and the specific rotation of the equilibrated solution 

 being + 55.3. This was the first of the disaceharides in which the ex- 

 istence of more than one form was demonstrated. 



Sodium amalgam reduces lactose, forming mannitol, dulcitol, lactic 

 acid, hexyl-alcohol and other products. Lactose is a glucose-galactoside 

 and not a galactose-glucoside, as shown by its behavior on gentle oxidation, 

 so that only the free aldehyde group will be oxidized. Under such con- 

 ditions lactobionic acid is formed, which on hydrolysis yields galactose and 

 gluconic acid, showing that the free aldehyde group is that of glucose, 

 while, if the free aldehyde group were that of galactose, galactonic acid and 

 glucose would result from the hydrolysis of the oxidation product. 



Lactose is much more difficultly hydrolyzed by acids than sucrose. It 

 is also hydrolyzed by the enzyme lactase, found in the intestinal mucose of 

 animals, as well as by aqueous extracts of kefir and some yeasts and al- 

 monds (crude emulsin). It is not hydrolyzed by maltase, invertase or 

 any enzymes in brewers' yeast. This serves as a simple means of distin- 

 guishing between lactose and glucose, a problem often met with by the path- 

 ological chemist, since glucose is readily fermented by yeast. Lactose also 

 forms a fairly characteristic osazone, which may be readily distinguished 

 from glucosazone. A good way to prepare the osazones from biological 

 material is to precipitate most of the interfering substances by adding 

 mercuric nitrate in dilute nitric acid solution and then solid sodium car- 

 bonate. Then filter, cover the filtrate and prepare the osazone in the usual 

 way with plienylhydrazine hydroehlorid and sodium nitrate. 



Maltose. Maltose or malt sugar is formed by the action of diastase 

 upon starch. The sugar was first isolated by DC Saussure in 1819, but its 

 identity was determined by Debninfaut in 1847 and he gave it the name 

 maltose. It occurs in plants and animal tissues to some extent, and re- 

 sults from the action of diastase of the pancreatic secretion, or ptyalin of 

 saliva on starch or glycogen. 



Maltose crystallizes in small needles with one molecule of water of 

 crystallization. It is easily soluble in. water and in alcohol its solubility 

 is 5 per cent. Its solutions show rnutarotation. Its specific rotation in- 

 itially is + 119 and that of the equilibrated mixture is + 137. 



