4O , PHYSIOLOGICAL CHEMISTRY 



and alcohol. This same reaction may occur in the alimentary canal as 

 the result of the action of putrefactive bacteria. In the preparation of 

 kephyr and koumyss the lactose of the milk undergoes alcoholic fermen- 

 tation, through the action of ferments other than yeast, and at the 

 same time lactic acid is produced. Lactose and galactose yield mucic 

 acid on oxidation with nitric acid. This fact is made use of in urine 

 analysis to facilitate the differentiation of these sugars from other re- 

 ducing sugars. Mucic acid is COOH(HCOH) 4 COOH. 



Lactose is not fermentable by ordinary baker's yeast. Mathews 1 

 has suggested an easy way to differentiate and determine lactose in the 

 presence of glucose based on reduction before and after fermentation 

 with yeast. 



EXPERIMENTS ON LACTOSE 



1-6. Repeat Solubility, Fehling's, Phenylhydrazine, Barfoed's, Nylander's 

 and Fermentation tests as given under Glucose, pages 21-31. 



7. Mucic Acid Test. Treat 100 c.c. of the solution containing lactose with 

 20 c.c. of concentrated nitric acid (sp. gr. 1.4) and evaporate the mixture in a 

 broad, shallow glass vessel on a boiling water-bath, until the volume of the mix- 

 ture has been reduced to about 20 c.c. At this point the fluid should be clear, 

 and a fine white precipitate of mucic acid should form. 



If the percentage of lactose present is low it may be necessary to 

 cool the solution and permit it to stand for some time before the pre- 

 cipitate will appear. It is impossible to differentiate between lactose 

 and galactose by this test, but the reaction serves to differentiate these 

 two sugars from all other reducing sugars. 



Differentiate lactose from galactose by means of Barfoed's test, 

 page 29. 



SUCROSE, Ci 2 H 22 On 



Sucrose, also called saccharose or cane sugar, is one of the most 

 important of the sugars and occurs very extensively distributed in 

 plants, particularly in the sugar cane, sugar beet, sugar millet and in 

 certain palms and maples. 



Sucrose is dextro-rotatory and upon hydrolysis, as before mentioned, 

 the molecule of sucrose takes on a molecule of water and breaks down 

 into two molecules of monosaccharide. The monosaccharides formed 

 in this instance are glucose and fructose. This is the reaction : 



; Sucrose Glucose Fructose 



This process is called inversion and may be produced by bacteria, en- 

 zymes, and certain weak acids. After this inversion the previously 

 strongly dextro-rotatory solution becomes levb-rotatory. This is due 



1 Mathews: Jour. Am. Med. Ass'n., 75, 1568, 1920. 



