I04 THE CARBOHYDRATES 



with iodine is red, and after digestion with diastase a reducing 

 sugar is found. A similar substance — termed soluble starch — 

 has been described as occurring in the epidermis of Saponaria 

 officinalis and also in Eungi. It must, however, be borne in 

 mind that the glucoside saponarin,* C.,^H.,^0,2, is not un- 

 common in the epidermis of leaves of many plants, e.g. Sapoti- 

 aria officinalis itself, and as it gives a blue to violet coloration 

 with iodine it is not unlikely that, in some cases, what has 

 been described as soluble starch is really saponarin. 



As already mentioned, the question of the formation of 

 dextrins from starch by the action of diastase has been the 

 subject of a great many researches, and has, at different times, 

 resulted in the postulation of the existence of a large variety 

 of dextrins and intermediate products, such as amylo-, achroo-, 

 erythro-, and malto-dextrin, amylases, amyloins, glyco- 

 amylins, etc., many of which did not survive for long. 



The chief facts observed during the action of malt extract 

 on starch may be very briefly summarized as follows. If, say, 

 a lo per cent starch paste is left in contact with malt extract 

 at 50°, the mass rapidly liquefies and the solution acquires a 

 sweet taste owing to the conversion of starch into maltose; if 

 the latter substance be estimated from time to time, it will be 

 found that the reducing power of the mixture increases rapidly 

 at first until, after about two hours, the amount of maltose 

 present corresponds to about 80 per cent of the starch em- 

 ployed, when practically no further change takes place. The 

 change in the starch paste can also be demonstrated by peri- 

 odic testing with iodine solution ; the blue-black coloration 

 gradually becomes less and less marked until various shades 

 of red are obtained, finally the iodine gives no distinctive 

 coloration. A corresponding fall in the optical activity of the 

 solution can also be observed, but as the activity is still greater 

 than what it should be for maltose alone, it must be concluded 

 that some other substance is formed at the same time as the 

 maltose, and that its reducing power is less but its activity is 

 greater than that of maltose. The amount of this " non-maltose " 

 product of diastatic activity varies directly with the tempera- 

 ture, and increases considerably at the expense of the maltose 

 if the temperature be kept at or above 60° ; if to such a pro- 



* Barger : " Ber. deut. chem. Ges.," 1902, 35, 1296. 



