COMPOSITION OF STARCH GRAINS 97 



he regarded as an anhydride which could be converted into the 

 soluble /3 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,* and Fernbach and Wolff,f 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 

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

 soluble form is produced by heating the insoluble one with 

 water under pressure, and the insoluble form may be recovered 

 from the solution by cooling, a process which is known as 

 " reversion ". The insoluble amylo-cellulose is probably iden- 

 tical with the substance described by Nageli under that name, 

 in that it is not coloured by iodine ; it is, however, not re- 

 garded as differing essentially from the soluble form (Niigeli's 

 granulose), but rather as being a polymer of it or a different 

 crystalline variety. 



The second constituent, amylo-pectin, is a mucilaginous 

 substance of an entirely different nature, which is not coloured 

 blue by iodine and dissolves in malt extract, without, however, 

 being converted into a sugar ; it swells up without dissolving 

 when heated with water. According to Maquenne | and 

 Roux, it is amylo-pectin which produces the gelatinization of 

 starch in the form of starch paste, which substance may there- 

 fore be regarded as a colloidal solution of amylo-cellulose 

 (amylose) thickened by an insoluble gelatinized slimy material, 



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



t Fernbach and Wolff: id., 1904, 138, 819. 



t Maquenne : " Bull. Soc. Cliim.," Paris, 1906, [3], 35, i, and "Ann. Chim. 

 Piiys.," 190 }, [8], 2, log; Maquenne and Roux; "Ann. Chim. Phys.," 1906, [8], 

 9. 179. 



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