DIGESTION. ACTION OF SALTS. 125 



Take half a tubeful, boil it at once, and when cool 

 dilute some of it and test with iodine, blue iodide, and 

 with Fehling no reduction. Soluble starch (B). 



Make two-thirds of a beakerful of a fresh digestion with 

 cleared mucilage provided for you, and which has been 

 obtained by allowing some more dilute mucilage to settle until 

 the uns welled grains and non-carbohydrate materials have 

 deposited. 



Prepare several tubes of weak iodine solution, by adding a 

 few drops of the solution to a half tube of water in each case. 



Test the digestion at frequent intervals by carrying a drop 

 of it with the thermometer into one of the tubes containing 

 iodine. Take specimens as follows, boiling each at once to 

 arrest further ferment action $-- 



When iodine gives a red port colour erythrodextrin (C). 



When iodine ceases to give this colour and Fehling 

 is not reduced achrodextrin (D). 



When Fehling gives a reaction maltose (E). 



Arrange the specimens behind their corresponding iodine 

 reactions in the tube stand ready for the next process. 



Precipitation of starch and its derivatives by neutral 

 salts. Form the iodides or use those already obtained and 

 saturate some of each with Am 2 SO 4 , or MgSO 4 . A pp results. 

 The pp occurs without the iodine, but more slowly. NaCl is 

 inactive. 



The crystalline carbohydrates dextrose, levulose, cane sugar. 

 Lactose and maltose do not yield this pp. (R. A. Young, 

 Jl. Physiology, Camb. and Lond., Vol. xxii., pg. 405.) 



Commercial dextrin (British gum, made by heating starch 

 to 200 C.). 



