302 PHYSIOLOGY OF NUTRITION. 



with Iodine solution after cooling, it is found that the first samples 

 on addition of the Iodine become violet, later ones reddish brown, 

 and still later one yellowish in colour. These colour reactions 

 show that under the influence of the acid, different kinds of 

 dextrins are formed from the starch in succession. First, the 

 starch substance breaks down into sugar and amylodextrin I., 

 which gives a violet reaction with Iodine. This dextrin is then 

 split up by the acid into sugar and amylodextrin II., which be- 

 comes reddish-brow^n on addition of Iodine. Still other kinds of 

 dextrin, colouring yellowish with Iodine, are formed together 

 with sugar from amylodextrin II., and finally the dextrins com- 

 pletely disappear, having been entirely converted into sugar. 1 

 According to recent researches the process is perhaps otherwise. 



That dextrins (and especially those which react brownish with 

 Iodine) occur in the cells of plants, we can determine in the 

 following manner. Pea seeds are ground to powder in a hand- 

 mill. We treat with a moderate quantity of water, and after an 

 hour pass pure Carbon dioxide into the turbid fluid. We then 

 filter, this operation being very much facilitated by the presence 

 of the Carbon dioxide. A small quantity of the clear filtrate is 

 next brought into contact with a crystal of Iodine, and we shall 

 find that the fluid by degrees assumes a brownish colour ; it be- 

 haves like an aqueous solution of commercial dextrin placed in 

 contact with Iodine. Pure water assumes in contact with solid 

 Iodine only a yellow tint. 8 If we investigate the behaviour of 

 the aqueous extract of pea seeds towards Fehling's solution, it is 

 seen that no reduction takes place. If, on the other hand, we 

 boil an aqueous extract for some time after adding a few drops of 

 Sulphuric acid, the fluid will be in a position to reduce Fehling's 

 solution energetically, since the dextrin under the influence of the 

 acid has been converted into glucose. 



1 See W. Naegeli, Beitrage zur nciheren Kenntniss der Stilrkegruppe, 1879, and 

 Detmer, Landicirthschaftl. Jahrbiicher, Bd. 10, p. 752. 



2 See Detmer, Journal f. Landwirtlischaft, 27. Jahrgang, p. 379. 



117. Estimation of and Microchemical Tests for Cane-Sugar. 



Cane-sugar is a constituent of the sap of many plants, and the 

 sap of the beetroot contains an especially large proportion of it. 

 To determine the quantity of sugar present in the roots, we follow 



