CH. VIII.] TYROSINASE. 233 



276. Horseradish peroxidase. Horseradish scrapings are 

 soaked in alcohol, filtered and dried in a thin layer. The dried 

 scrapings are extracted with water and filtered. Place 2 or 3 cc. 

 in labelled test-tubes and try the following experiments, a few drops 

 of guiacum tincture or of 10 volumes hydrogen peroxide where 

 indicated. 



A. Extract 4- guiacum. 



B. Extract + guiacum + H 2 O 2 . 



C. Guiacum + H 2 O 2 . 



D. Boiled extract + guiacum 4- H 2 O 2 . 



If satisfactory reagents are employed a blue colour is only 

 produced in B. 



277. Potato tyrosinase. Prepare an extract of potato peel 

 as described in Ex. 274. Boil a little tyrosine with about 5 cc. of 

 distilled water and cool to about 40 C. Make the following mix- 

 tures : 



A. Extract + tyrosine suspension. 



B. Extract alone. 



C. Boiled extract + tyrosine suspension. 



Incubate at 37 C. and note the appearance at intervals. Both 

 A and B darken, but A much more than B. 



