284 PRACTICAL PHYSIOLOGY 



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

 formula. 



lOOa 



" 8l 



where s = (a)D. 



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

 (e.g. urine) the polar imeter 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 * of certain of the sugars is as follows : 



Monosaccharides : Dextrose : +52 *7. 



Galactose : +81. 



Laevulose : -93. 



Invert sugar : - 20 '2. 



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

 hydrolysed. 



Cane sugar : + 66 '5 after hydrolysis becomes laevorotatory (vide invert sugar). 

 Maltose : + 137 after hydrolysis becomes much less. 

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



IV. Mowe'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 (CH 3 - CO - CH 2 - CH 2 - COOH). 



EXPERIMENT III. Mix equal quantities of a 1 % solution of 

 dextrose, and 40 % NaOH in a test tube ; heat. A yellow to brown 

 colouration results, and an odour of burnt sugar (caramel) is produced. 

 This odour becomes very evident if, after qpoling, the solution be 

 acidified with H 2 S0 4 . 



The Chief Monosaccharides are dextrose, laevulose and galactose. 



Dextrose, grape sugar or glucose (C 6 H 12 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 O'l to O15 %, but in disease it may rise 

 to such a degree that it appears in detectable amount in the urine 

 (see p. 447). Commercially it exists as a syrup much used in making 

 confections. It is easily crystallised. 



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 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 laevulose and 

 invert sugar. 



