76 PHYSIOLOGY. 



this add i to 2 cc. of cobaltous nitrate solution (5 grams cobalt nitrate in 100 

 cc. distilled water. Keep in a stoppered bottle), then add a small quantity 

 of a strong sodium hydrate solution (50 grams caustic soda, in sticks, to 

 100 cc. distilled water. Keep in a bottle). A beautiful violet color appears. 

 Test glucose or grape sugar in the same way and a blue color appears, 

 which gradually changes to green. 



157c. Cane sugar (sucrose) can be changed to glucose or invert sugar 

 in the following way: To a weak solution of pure granulated cane sugar 

 in a small beaker add a few drops of strong hydrochloric acid, rest on gauze 

 wire, and boil for a minute or two over a flame. This inverts the cane 

 sugar to glucose (equal parts of dextrose and laevulose). To test for the 

 invert sugar the acid must be neutralized. Add sodium carbonate until on 

 adding no effervescence takes place. Now add the Fehling's solution and 

 boil; the red precipitate appears, showing that it reduces Fehling's solution. 

 158a. Tests for sugar in plant tissue. Scrape out a little of the tissue 

 from the inside of a ripe apple or pear, place it with a little water in a test 

 tube, and add a few drops of Fehling's solution. After standing half an 

 hour the characteristic precipitate of copper and cuprous oxide appears, 

 showing that grape sugar is present in quantity. 



Make thin sections of the apple and mount in a drop of Fehling's solution 

 on a slide. After an hour examine with the microscope. The granules 

 of cuprous oxide are present in the cells of the tissue in great abundance. 



1586. Prepare another tube with some of the pulp in 15 cc. of water; 

 add 2 cc. of cobaltous nitrate solution, and then some of the strong sodium 

 hydrate solution, as in paragraph 157^. Cane sugar as well as grape 

 sugar is present in these fruits. 



158c. Cut up several leaves of a vigorous young Indian corn seedling 

 in a small beaker and add 25 or 30 cc. distilled water. Boil for one or 

 two minutes. Filter. In another small beaker boil Fehling's solution, 

 and if it is free from sediment (if not, filter) add a portion of the filtered 

 corn-leaf solution and boil for two minutes. Hold the beaker toward the 

 light and look on the bottom for the red precipitate. Filter. The red 

 precipitate shows the presence of glucose (or invert sugar). Take the 

 remaining portion of the corn-leaf decoction in a test tube and test for cane 

 sugar by adding cobaltous nitrate and sodium hydrate as in paragraph 

 1576. If the violet color does riot appear at once, do not agitate it, but 

 allow it to stand for a while. The violet color appears at the bottom of the 

 tube, showing the presence of cane sugar, while the reaction for glucose may 

 appear in the upper portion of the solution. For comparison take similar 

 corn leaves, remove the chlorophyll with alcohol, and test with iodine. No 

 starch reaction appears. The carbohydrate in corn leaves is therefore sugar 

 and not starch. If now the grain of corn be examined the cells will be 

 found to be full of starch grains, which give the beautiful blue reaction 



