32 



CARBOHYDRATES 



CHO 



1 



HCOH 



I 

 HOCH 



I 

 HCOH 



I 

 HCOH 



I 

 CH2OH 



D-Glucose 



CH=NNHC6H5 



I 

 C=NNHC6H6 



+ SCeHjXHNHi 

 (phenylhydrazine) 



HOCH 



I 

 HCOH 



I 

 HCOH 



+ CeHsNHj + 2H2O + NH3 



Aniline 



CH2OH 



D-Glucosazone 



This precipitate is made up of long yellow needles, usually arranged in 

 a broom-like or sheaf structure. The osazone is frequently of great 

 help in establishing the presence of glucose in a digestion product, fruit 

 juice, or other saccharine substance. It cannot be relied upon alone, how- 

 ever, because all reducing sugars give osazones. In fact, D-fructose and 

 D-mannose produce the same osazone as D-glucose does. In many cases, 

 however, the crystalline form, and more particularly the optical rota- 

 tion and melting point of the osazones, are of great help in identifying 

 individual sugars. 



D-Galactose 



Galactose does not occur free in nature but is found combined with 

 other sugars in many carbohydrates and related compounds. Each of 

 the sugars, lactose and raffinose, gives one molecule of galactose on 

 hydrolysis, and certain polysaccharides, the galactans, yield galactose 

 as the chief hydrolytic product. Legumes, impure pectin, agar, and 

 Douglas fir and other coniferous woods are other galactose-yielding ma- 

 terials. Galactose is also a constituent of certain galactosides found in 

 brain and nerve tissue, and of many animal proteins. Its occurrence 

 in these physiologically important tissues gives to galactose added sig- 

 nificance and importance. 



Galactose is generally made from lactose by hydrolysis and crystalliza- 

 tion. Aside from the small amount required by bacteriological labora- 

 tories for the study of the fermentation characteristics of bacteria, there 

 is no particular demand for it. 



Most bread yeasts do not ferment galactose, but many wild yeasts 

 ferment it readily. Bacteria, generally speaking, attack it more slowly 

 than either glucose or fructose. Being an aldose, galactose reduces 

 Fehling's solution and gives a characteristic osazone with phenylhydra- 

 zine. 



The most distinctive property of galactose is the formation, when 



