120 THE CARBOHYDRATES 



Action of Bacteria on Starch. 



By the action of Bacillus macerans on 5 per cent starch 

 paste, Schardinger* has obtained two crystalline substances 

 which he describes as a and /3 dextrin, the former of which 

 gives with iodine a dark green compound crystallizing in 

 needles, whilst the latter gives dark red-brown prisms. Prings- 

 heim and Langhans f ascribe to these compounds the formulae 

 (C 6 H 10 O 5 ) 4 and (C 6 H 10 O 5 ) 6 respectively ; they have obtained 

 from the former a crystalline disaccharide (C 6 H 10 O 5 ) 2 , and from 

 the latter a crystalline trisaccharide (C 6 H 10 O 5 ) 3 . All these 

 four compounds have a sweet taste and, according to the 

 authors, they are representatives of a new class of crystalline 

 polysaccharides which they term amyloses. \ The substances 

 are accordingly named di-, tri-, tetra-, and hexa-amylose. In 

 a subsequent communication Pringsheim and Eissler describe 

 two further substances, isotriamylose and isbdiamylose, which 

 are isomeric with tri- and diamylose respectively. 



Reactions. 



1. The appearance of the grains under the microscope 

 and their action on polarized light in the presence of water 

 are well known. 



2. The most characteristic reaction of starch is the blue 

 colour produced with iodine. The composition of this blue 

 substance varies ; it contains, on an average, about 18 per cent 

 iodine, and cannot be formed unless a small quantity of hydri- 

 odic acid, which is always present in small amounts in ordinary 

 solutions of iodine, be present. The blue colour is discharged 

 on heating the solution, but reappears on cooling. The dried 

 substance may, however, be heated to 100 without under- 

 going alteration. It is stated that those parts of the grain 

 which are particularly rich in granulose are the most affected 

 by the iodine. 



If the starch grains are very small, or relatively so few in 

 number that they might easily be overlooked, Meyer's pro- 



* Schardinger : " Zeitsch. f. Natur. u. Genussm.," 1903, 6, 874. 



f Pringsheim and Langhans : " Ber. deut. chem. Ges.," 1912, 45, 2533. 



% The choice of this term is unfortunate in view of the various uses to which 

 it has already been put by other authors, such as Meyer, Maquenne, and Roux, 

 etc. (see pp. 115, 116). 



Pringsheim and Eissler : " Ber. deut. chem. Gesells.," 1913, 46, 2959. 



