44 The Fermentation of Cacao 



colour within a short time, while boiled seed 

 thus treated will not show any change of colour, 

 even after many hours' exposure to the air. 

 This is in full analogy with similar phenomena 

 observed very frequently with plants, and is 

 due to the presence of oxidases or oxidizing 

 enzymes. When cells are killed by being cut 

 open or in any other way that will not injure 

 the oxidases, these will, upon the death of the 

 protoplasm in which they are stored up, be 

 liberated and at once commence their activity, 

 easily recognized by the early appearance of a 

 brown, black, or red colour. These colours 

 are often due to the oxidation of various 

 kinds of tannins originally present in the juice 

 or cell sap. 1 If, however, the death of the 

 protoplasm is produced by strong acids or 

 boiling temperature, 2 the oxidases will also be 

 killed and no colour change will be noticed, as 

 the tannins and other readily oxidizable matters 

 in the juices cannot easily take up the 

 atmospheric oxygen without the assistance of 

 oxidases. 



A further control experiment was made in 

 which the pulped cacao (seed with testa and 

 attached slime layer) was boiled for about 

 twenty minutes with a 2 per cent, dilute sul- 

 phuric acid. The slimy tissue contracted, and 



1 Such a case is observed in the curing of tobacco, 

 whereby a fine brown colour is produced. 



2 The killing temperature for oxidases is 20 to 30 C. 

 higher than that for protoplasm or living matter. 



