34 PHYSIOLOGICAL CHEMISTRY 



and uniformly light." The difference between this reading and the 

 zero is a or the observed rotation in degrees. 



Sugar solutions (glucose, levulose, lactose, maltose, but not sucrose) 

 when freshly prepared possess a changing rotation, so called mutarotation. 

 For this reason such solutions before polariscopic examination should 

 be allowed to stand over night, heated to iooC. and then cooled, or 

 treated with a drop of ammonia followed by a drop of acid. 



Polarizing saccharimeters are also constructed by which the per- 

 centage of sugar in solution is determined by making an observation 

 and multiplying the value of each division on a horizontal sliding scale 

 by the value of the division expressed in terms of dextrose. This 

 factor may vary according to the instrument. 



"Optical" methods embracing the determination of the optical 

 activity are being utilized in recent years in many "quantitative" 

 connections. l 



CH 2 OH 



I 

 FRUCTOSE (CHOH) 3 



CO 



:H 2 OH 



As already stated, fructose, sometimes called levulose or fruit sugar, 

 occurs widely disseminated throughout the plant kingdom in company 

 with glucose. Although it is a ketose it nevertheless reduces metallic 

 oxides in alkaline solution due to the presence of the terminal group 

 CO CH^OH. For the same reason monohydroxyacetone (CH 3 CO-- 

 CH2OH) also reduces such solutions although acetone (CH S CO CHs) 

 does not. The reducing power of fructose is somewhat weaker than 

 that of dextrose. Fructose does not ordinarily occur in the urine in 

 diabetes mellitus, but has been found in exceptional cases. With 

 phenylhydrazine it forms the same osazone as glucose. With me thy 1- 

 phenylhydrazine, levulose forms a characteristic methylphenylfruc- 

 tosazone. 



(For a further discussion of fructose see the section on Hexoses, 

 page 20.) 



EXPERIMENTS ON FRUCTOSE 



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

 and Fermentation tests as given under Glucose, pages 21-32. 



Abderhalden and Schmidt: "Determination of blood content by means of the optical 

 method," Zeit. physiol. Chem., 66, 120, 1910; also C. Neuberg: "Determination of nucleic 

 acid cleavage by polarization," Biochemische Zeitschrift, 30, 505, 1911. 



