COMPOSITION OF STARCH GRAINS 115 



blue colour with iodine, but it is doubtful whether the liquid is 

 a true solution ; it is more likely a colloidal solution in which 

 the particles are sufficiently small to pass through the pores of 

 the filter paper. 



With regard to the chemical nature of starch granules there 

 are considerable differences of opinion. The researches of Nageli 

 have shown that when starch is treated with dilute hydrochloric 

 acid, malt extract, or saliva, a considerable portion goes into 

 solution, leaving a transparent skeleton undissolved. The 

 soluble portion, which gives a blue colour with iodine, Nageli 

 regarded as the true starch constituent of the granule, and 

 named it granulose ; on the other hand, the undissolved skele- 

 ton, which is not turned blue by iodine, he considered to be 

 of a cellulose nature, and called it starch cellulose or amylo- 

 cellulose. 



On the other hand, Meyer * was of opinion that starch 

 granules consisted essentially of two substances known respec- 

 tively as a and /3 amylose. The former, which was insoluble, 

 he regarded as an anhydride which could be converted into the 

 soluble ft variety by the action of superheated steam. 



He also thought that when starch is acted upon by hydro- 

 chloric acid it is converted into amylo-dextrin, and considered 

 that amylo-cellulose, which Nageli regarded as an original 

 constituent of the starch granule, was in reality identical with 

 amylo-dextrin, and therefore a secondary product of the action 

 of acid on the amylose. 



According to the view of recent workers, notably Maquenne 

 and Roux,fand Fernbach and Wolff, J starch granules consist 

 of two substances : amylo-cellulose, or amylose, as they describe 

 it later, and amylo-pectin. The term amylo-cellulose is, how- 

 ever, employed in a different sense from that assigned to it by 

 Nageli. It is, according to these authors, the principal consti- 

 tuent, and is partly soluble in boiling water and completely 

 soluble in water under pressure; in solution it gives a blue 

 colour with iodine, and is converted into maltose by malt, but 

 the solid state it is not acted upon by these reagents. The 

 >luble form is produced by heating the insoluble one with 



* Meyer: " Unters u. d. Starkekorner," Jena, 1895. 



t Maquenne and Roux : " Compt. rend.," 1903, 137, 88; 1905, 140, 1303. 



$ Fernbach and Wolf: id., 1904, 138, 819. 



8* 



