52 INTRODUCTION. 



ing in a physiological point of view, from the fact that much 

 of the sugar which disappears in the economy is now thought 

 to undergo this change. 



A clear solution of sugar has a peculiar effect upon polar- 

 ized light, being possessed of what is called a rotatory power. 

 If a ray of polarized light be passed through a tube contain- 

 ing simple water, its direction is unchanged ; but if a saccha- 

 rine solution be substituted, it is found to possess what is 

 called molecular activity, and turns the ray to the right. The 

 amount of deviation, which can easily be measured by an 

 instrument constructed for this purpose by Biot and Soleil, 

 called a polarimeter, indicates the quantity of sugar in the solu- 

 tion. The instrument above mentioned is sometimes used 

 for quantitative analysis. 



Tests for Sugar. Keliable tests for determining the 

 presence of sugar in the animal tissues and fluids are useful 

 to the practical physician as well as the physiologist; for 

 this substance frequently occurs in the urine, as a pathological 

 condition, when it is essential to ascertain the fact of its 

 presence, even if no attempt be made to determine its quan- 

 tity. For this purpose a number of tests have been devised, 

 which are most of them reliable and simple of application. 



Moore's, or the Potash Test. This test depends on the 

 conversion of the animal sugars into melassic acid by boiling 

 with a caustic alkali. It is employed in the following way : 

 To a small portion of the suspected liquid in a test tube we 

 add a little caustic potash in solution, and boil the mixture. 

 If sugar be present, a brownish color will be produced, its 

 intensity depending upon the quantity of sugar. This test 

 is applicable only to glucose, grape sugar, and the animal 

 varieties. 



Trommels Test. This is one of the most delicate and 

 convenient tests for sugar. It is employed in the following 



