272 CONTENTS AND PRODUCTS OF CELLS 



453. Other cell contents are the proteids. There is a large 

 number of different proteids. They are very complex organic 

 products composed of carbon, oxygen, hydrogen, nitrogen, 

 and in addition sometimes phosphorus and sulfur. The 

 white of egg is a proteid. The protoplasm itself is a proteid. 



454. Of the various sugars in the cell, glucose or grape- 

 sugar, so named because it is so abundant in grapes, is 

 perhaps the most common in plants (179). It is probably 

 the first carbohydrate formed in the plant, and the one 

 from which all others are derived. It is also a product of 

 the digestion of maltose, which in turn is derived from the 

 conversion of starch in the plant. It is also one of the sugars 

 formed from the digestion of cane sugar. It is very soluble 

 and therefore is in a convenient form for transportation 

 from one part of the plant to another. Corn syrup is glucose 

 derived from starch of the corn kernel. 



455. To test for glucose: Make a thick section of a bit of 

 the edible part of a pear and place it in a bath of Fehling's 

 solution. After a few moments, boil the liquid containing 

 the section for one or two minutes. It will turn to an orange 

 color, showing a deposit of an oxid of copper and perhaps 

 a little copper in the metallic form. A thin section treated 

 in like manner may be examined under the microscope, 

 and the fine particles, precipitated from the solution by the 

 sugar of the pear, may be clearly seen. Fructose and maltose, 

 as well as other organic substances, give a similar reaction 

 with Fehling's solution. In the case of fruits and other com- 

 mon products, it may be assumed that precipitation of the 

 oxid of copper is due to glucose or fructose. With barley 

 malt, the precipitation of the copper oxid is due to maltose. 

 Test various fruits by boiling them in water in a test-tube, 

 and then determine whether sugar is present by adding 

 Fehling's solution to the extract and again heating. Feh- 

 ling's solution is made by taking one part each of these three 

 solutions and two parts of water: (1) Copper sulfate, 9 



