REACTIONS OF SUGARS NITRATES. 67 



gas flame, till small bubbles commence to form in the fluid. By 

 this time the section will have become a beautiful vermilion-red 

 colour from the presence of reduced copper protoxide, which can 

 be seen in the cells under the microscope in the form of very 

 numerous grains. There is present in the cells of the pear, 

 therefore, a substance which reduces the alkaline copper oxide 

 solution, a substance belonging to the grape-sugar group (glu- 

 coses), in this particular case grape-sugar or Isevulose, 



For comparison we repeat the experiment with a section of 

 beetroot. 1 This contains, as is well known, a member of the 

 cane-sugar group, viz., Cane-sugar. Heated in the same way in 

 Fehling's solution this shows no precipitate in the cells ; under 

 the microscope the section has a blue colour. If the section is 

 boiled for a longer time in the solution it begins to be coloured 

 vermilion-red on the surface ; the cane-sugar is inverted, i.e., 

 converted into glucose, by the strongly alkaline reagent, and now 

 gives the protoxide precipitate. Under the microscope the peri- 

 pheral cell-layer now shows the vermilion-red grains, while, 

 provided the action has not been too prolonged, the inner cells 

 still show the blue colour due to the presence of cane-sugar. 



Reaction for Nitrates. We will once more use the Beetroot, 

 in order to realise the micro-chemical reactions for nitrates by 

 means of diphenylamine. This reagent, used by the chemist for 

 the detection of very small quantities of nitrates and nitrites, 

 serves excellently for histological purposes. We prepare cross 

 or longitudinal sections through the beetroot, taking care, how- 

 ever, that the sections extend to the surface. We can, with 

 advantage, allow the sections to previously become somewhat 

 dry on the object -slide, and then add the reagent. We use 0*05 

 gram, diphenylamine in 10 c.cm. pure sulphuric acid. Immediately 

 after the addition of this a deep blue coloration (formation of 

 aniline blue), shows in the outermost zone of the section. This 

 zone contains the youngest tissue of the root, still in course of 

 development ; it is this, therefore, which contains the nitrate. 

 From these parts the colour quickly flows over the rest of the 

 preparation, but in the first moment of the reaction the coloured 

 zone is often sharply delimited. Nitrites, and various other salts, 

 appear to give the same reactions, but ash analyses tend to show 



1 Red beetroot can be freely used for this reaction, as the red colour 

 disappears at once with action of the reagent. Or the parsnip may be used 

 in its stead. [ED.] 



