Ii6 THE ACTION OF ENZYMES 



colour immediately, but the colour does not develop until 

 hydrogen peroxide is added if a peroxidase only is present. 



Ex. 66. Make a tincture of gum guaiacum by adding a 

 few lumps of this substance to a test-tube or flask containing 

 alcohol; boil for some time, and to the yellow solution add 

 water cautiously until near the point at which a permanently 

 milky emulsion is formed. If too much water is accidentally 

 added, and the solution remains milky, it may be cleared by the 

 addition of a few drops of alcohol. 



(a) Cut thin slices of apple, potato, and mangel, and place 



them in small portions of the guaiacum solution. 

 Note the production of a blue colour. 



(b) Try the experiment with slices which have been boiled for 



five minutes. 



(c) Add the juice from raw beef to some of the solution, and 



note if a blue colour is produced ; if not, try the 

 addition of a few drops of hydrogen peroxide. 



An enzyme termed catalase is very widely distributed 

 in the protoplasm of all living animals and plants, and 

 is also found in many bacteria. It has the power of 

 liberating oxygen from hydrogen peroxide, but the 

 oxygen set free does not give a blue colour with tincture 

 of guaiacum. 



Ex. 67. 



(a) Pour some hydrogen peroxide solution over the surface 



of an agar plate culture of several different kinds of 

 bacteria, and note the evolution of bubbles of oxygen. 

 Where are the bubbles most abundant ? 



(b) Try the same experiment, using the tincture of guaiacum 



and hydrogen peroxide mixture of Ex. 66. Is any 

 blue colour produced? 





