62 HYDROOARBONACEOUS PROXIMATE PRINCIPLES. 



QUANTITY OF SUGAR IN 100 PARTS IN 



Cherries . . . 18.12 Wheat flour . . . 2.33 



Apricots . . . 16.48 Rye flour . . . 3.46 



Peaches . . . 11.61 Barley meal . . . 3.04 



Pears .... 11.52 Oatmeal . . . 2.19 



Juices of sugar-cane . 18.00 Indian corn meal . . 3.71 



Sweet potatoes . . 10.20 Cow's milk . . . 5.20 



Beet roofs . . . 8.00 Goat's milk . . .5.80 



Parsnips . . . 4.50 Beefs liver . . . 1.79 



The three principal varieties of this substance which are most impor- 

 tant in a physiological point of view are glucose, cane sugar, and milk 

 sugar. 



Glucose, C G H 12 6 . 



Glucose, also called grape sugar from its abundance in the juices of 

 the ripe grape, may be considered as the most marked and representa- 

 tive variety of the saccharine substances. It occurs more frequently 

 than any other in the animal fluids, being found in the juices of the 

 liver, in the chyle, the blood, and the lymph. In diabetes it is abund- 

 antly excreted with the urine. It is also found in the juices of many 

 plants, in various sweet fruits, and in honey, where it is associated with 

 certain other varieties. It is freely soluble in water. Its solution has 

 a moderately sweet taste, and deviates the plane of polarization toward 

 the right 53.5. 



It is this form of sugar which is produced from starch by boiling with 

 dilute acids, by the action of the digestive fluids of the alimentary canal, 

 and in the plant during the process of vegetation. The change consists 

 in the assumption by starch of the elements of water in due proportion, 

 the new substance thus produced being still a carbo-hydrate. The 

 transformation of starch into glucose is therefore represented as 

 follows : 



Starch. Water. Glucose. 



C 6 H 10 5 + H 2 = C 6 H W 6 - 



Glucose may be recognized in solution by various well-marked tests. 

 First, the action of alkalies at a boiling temperature. If a solution of 

 glucose be treated with a solution of potassium hydrate and heat applied, 

 the sugar is decomposed and the liquid assumes, first, a yellowish and 

 then a brown color, which becomes deeper in proportion to the amount 

 of glucose and alkali existing in the solution. This is not a certain test 

 for the presence of glucose, as some other organic matters are discolored 

 in a similar way by the strong alkalies ; but it will serve to distinguish 

 it from certain varieties of sugar, which do not possess this property. 



Secondly, the test most commonly employed for detecting glucose 

 depends upon its power of reducing the salts of copper in a boiling 

 alkaline solution. This test, which is known as " Trommer's test," is 

 applied in the following manner: A very small quantity of copper 

 sulphate in solution should be added to the suspected liquid, and the 



