ii6 THE CARBOHYDRATES 



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 (Nageli'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, 

 the amylo-pectin. Amylo-pectin, moreover, tends to retard the 

 reversion of soluble amylo-cellulose into the insoluble form, and 

 hence there is a quantity of the soluble form present in the starch 

 granule which is able to dissolve in boiling water ; when, how- 

 ever, the amylo-pectin is removed, the pure insoluble amylo- 

 cellulose or amylose (as the authors prefer to call it) is 

 produced, f 



A new form of soluble starch has recently been described 

 by Fernbach.J: It is obtained by pouring a I or 2 per cent 

 aqueous suspension of potato starch into a large excess of pure 

 acetone and shaking vigorously ; a flocculent precipitate is 

 thus obtained, which, when filtered and ground up in a mortar 

 with more acetone and then dried in a vacuum, yields a light 

 white powder which is completely soluble in cold water. The 

 aqueous solution passes through filter paper and yields a very 

 pure blue colour with iodine. 



Brief mention may be made of the ideas held regarding the 

 physical nature of starch grains. As is well known, the gran- 



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

 Phys.," 1904, [8], 2, 109; Maquenne and Roux: "Ann. Chim. Phys." 1906, [8], 



9 I 79- 



t See also Gruzewska: " Journ. Phys. Path. Gen.," 1912, 14, 7. 

 JFernbach: " Compt. rend.," 1912, 155, 617 



