VIII] AROMATIC COMPOUNDS 125 



material which may be used for the above tests is fruit of the Melon and Cucumber 

 and root of the Kadish and Turnip. 



Of the above substances only guaiacum, as a rule, is sufficiently 

 sensitive to be oxidized by the amount of active oxygen produced by the 

 plant oxidase. The juices and water extracts of oxidase plants will usually 

 blue guaiacum immediately. If considerable quantities of sugars or 

 tannins are present in the tissues, they may inhibit the guaiacum 

 test. 



Another test which may be used is the following. A solution of 

 dimethyl -jo-phenylenedidmine hydrochloride and a-naphthol in presence 

 of dilute sodium carbonate gives a deep violet-blue colour in the presence 

 of an oxidase. 



Expt. 119. Demonstration of the presence of an oxidase. Cut two or three thin 

 slices from a fresh tuber of the Potato, pound well in a mortar, add a little water 

 and filter. With a few c.c. of the extract in an evaporating dish make the following 

 tests : 



(a) Add a few drops of 10 ^/o solution of guaiacum. A blue colour appears. 



(6) Add 2*5 c.c. of a 0*14 % solution of a-naphthol and 2 '5 c.c. of a 0*17 7o solution 

 of dimethyl -jo-phenylenediamine hydrochloride and 5 c.c. of 0*1 °l^ solution of sodium 

 carbonate. A deep violet-blue colour appears. 



Control experiments should be performed by using boiled enzyme extract. Other 

 material which may be used is fruit of the Pear, Plum and Cherry. 



Expt. 120. To show the distribution of oxidases and peroxidases in various plants^ 

 and the correlation between the presence of oxidase and browning on injury or in 

 chloroform vapour. Take a selection of the plants given below, and in each case grind 

 up a portion of the plant in a mortar with a little water and filter. Divide the filtrate 

 into two parts in small porcelain dishes. Allow one part to stand in air, and note the 

 darkening in colour in cases where an oxidase is present. To the other add a few 

 drops of guaiacum. To extracts containing a peroxidase only, after 5-10 minutes, 

 add in addition a few drops of hydrogen peroxide. Further, small pieces of the plants 

 to be tested should be placed in a corked flask containing a few drops of chloroform, 

 and the development of browning noted in the case of plants containing an oxidase. 

 For demonstration of oxidases the following plants may be used : Christmas Rose 

 {Helleborus niger)^ Dandelion {Taraxacum offi^cinale), Forget-me-not {Myosotis), 

 Hawthorn {Crataegus) and White Dead Nettle {Lamium album). For peroxidases : 

 Arabis, Aubrietia, Pea {Pisum sativum), Stock {Matthiola\ Wallflower {Cheiranthus 

 Chdri) and Violet ( Viola). 



The peroxidases, like other enzymes, can be extracted either with 

 water or dilute alcohol and precipitated from solution by strong alcohol. 



Expt. 121. Preparation of peroxidase from Horse-radish (Cochlearia) roots. Mince 

 up the Horse-radish roots in a mincing machine. The product is allowed to stand for 

 24 hrs. to enable the glucoside, potassium myronate, to be hydrolyzed by the enzyme, 

 myrosin. Then extract with 80 % alcohol. The alcohol is decanted off, and the 



