214 PRACTICAL PHYSIOLOGY 



To estimate the percentage of sugar in urine the chief precautions are, (1) to 

 see that it is perfectly clear, and (2) to see that it contains no protein. 



In order to obtain a specific or comparative number (i.e. a result always 

 obtained under the same conditions) it is necessary to adopt a standard. This 

 consists of the rotation, in degrees of a circle, produced by 1 gr. of the substance 

 dissolved in 1 c.c. of fluid and contained in a tube 1 dcm. long. This is called 

 the specific rotatory power and is represented by (a)D. 1 It is determined 

 by .the following formula: 



(a)D = + _?_ 

 ~p X I 



where a = the observed rotation, 



I = the length, in decimeters,of the tube in which the solution is placed, 



p = the weight, in grammes, of the substance contained in 1 c.c. solvent. 



The rotation produced by a substance depends upon its concentration in a 



solution ; if, therefore, the index (a)D of any substance be known, and its 



rotation be ascertained, its percentage P in any fluid can be ascertained by the 



formula : 



p _ lOOa 



^r 



where s = (a)D. 



For rapidly and accurately determining the percentage of sugar in any fluid 

 (e.g. urine) the polarimeter and especially that form of it in which the scale 

 reads percentages of sugar is a very valuable instrument. It is much used 

 for this purpose in the continental clinics. 



The Specific Rotatory Power 2 of certain of the sugars in about 10 per cent, 

 solution is as follows : 



Monosaccharides : Dextrose : + 52-7. 

 Galactose : +83. 

 Lsevulose : 93. 



Disaccharides. The (a)D of these carbohydrates changes when they are 

 hydrolysed. 



Cane sugar : + 66-5 after hydrolysis becomes Isevorotatory. 



Maltose : + 138 after hydrolysis becomes much less. 



Lactose : + 52-5 after hydrolysis becomes slightly more. 



IV. Moore's Test. -When heated with caustic soda a dark 

 substance called caramel is produced. This is also produced when 

 sugar is burnt. Caramel contains several chemical bodies, the most 

 important of which is an acid called levulinic acid. 



Quantitative methods for the estimation of sugar will be found 

 on pp. 275 and 292. 



The Chief Monosaccharides are dextrose, laevulose and galactose. 



Dextrose, .grape sugar or glucose (C 6 H 12 O 6 ), is found in many 

 fruits, and is an important food-stuff. In the healthy animal body 

 it occurs in the blood and muscles. In normal human blood the 

 amount of glucose is usually from 0-1 to 0-15 per cent. 



It is soluble in water and in alcohol. It has only a slightly sweet 

 taste. It rotates polarised light to the right ( (a)D = + 52-7). 



1 The " D " indicates that sodium light is used. 



2 The rotatory power of a solution of a sugar is frequently different when 

 the solution is freshly made from what it becomes on standing. This pheno- 

 menon is called mutarotation. The figures given are all for solutions which 

 have been kept long enough to be in equilibrium. Temperature also affects 

 the rotatory power of a solution, particularly in the case of Isevulose and 

 invert sugar. 



