The Last Word 261 



discolouration, and the cause of this change in 

 colour is brought about by the oxidation of the 

 tannic substances (possibly preceded by a split- 

 ting up of glucosides). 



It has often been suggested that oxidases 

 may play a part in the preparation of cacao. 

 Indeed, it is easy to prove that such is the 

 case. The oxidation of the tannin in other 

 fruits containing that substance is also put 

 down to oxidase. If fresh, decorticated cacao- 

 beans are crushed in water, the watery extract 

 gives a blue colour reaction with tincture of 

 guaiacol, and a dark blue reaction with an 

 aqueous solution of tetramethyl-paraphenylen- 

 diamin hydrochloride. These reactions are 

 best obtained by the capillary method of 

 J. Gruess. 1 



The oxidase action may be demonstrated 

 without the aid of foreign chemical substances. 

 If cacao-beans be heated in water to 75 C. 

 and then crushed, no change in colour and no 

 reduction of the bitter taste is produced in the 

 mass, whilst brown discolouration still occurs 

 after heating at 70 C. for an hour. The 

 browning of the beans heated to 70 C. can 

 still be obtained if a small amount of aqueous 

 extract of fresh cacao-beans be stirred into the 

 mass. For comparison, another portion of 

 the mass may be treated with a similar extract 

 previously heated to 80 to 100 C. ; in this 



1 " Bericht der deutschen botanischen Gesellschaft," 

 Bd. xxvi, p. 624. 



