74 THE ACTION OF ENZYMES 



About 8 i percent, of maltose and 19 per cent, of dex- 

 trin are found when the reaction is at an end. Under 

 certain conditions diastase will convert the dextrin into 

 maltose, so that the complete and final hydrolysis of 

 starch by this enzyme results in the formation of maltose 

 only. In all cases, however, a number of intermediate 

 dextrins are first produced, and it is to the presence of 

 these that the colour changes, previously mentioned, are 

 due, the purple colour being given by starch and a cer- 

 tain amount of one or more kinds of dextrin, the reddish 

 brown tint by the latter in the absence of starch, the 

 final products, namely, maltose and dextrin, being 

 uncoloured by iodine. 



Many pathogenic bacteria are able to produce amylo- 

 lytic or starch-splitting ferments ; Bs. subtilis, Bs. mega- 

 therium, Clostridium butyricum, and other butyric bacteria, 

 as well as species of Proteus and bacteria isolated from 

 cereal grains and soil, have been found to yield enzymes 

 of this class also. 



Ex. 39. Cut thin sections from a piece of potato tuber and 

 from a wheat grain : examine with a low power and make draw- 

 ings of the starch-grains within the cells observed. 



Ex. 40. Make a strong solution of potassium iodide in water 

 and add to it a few crystals of iodine. Allow the mixture to 

 stand for twelve hours, and shake occasionally in order to 

 facilitate the solution of the iodine. When the latter is all 

 dissolved, add more water until the whole is the colour of dark 

 sherry. 



When examining the starch-grains place a drop of this solution 

 near the edge of the cover-slip so that it may run under the 

 latter and come in contact with the starch-grains. Note the 

 change in colour of the starch-grains. 



Ex. 41. Make an extract of malt diastase as follows : Shake 



