ADULTERATION OP WHEAT-FLOUR. 345 



starch will immediately swell up, and acquire three or four 

 times their natural size ; while those of the wheat-starch 

 are scarcely affected by it ; if adulterated with pea or bean 

 meal, the hexagonal tissue of the seed is at the same time 

 rendered very obvious under the microscope. Polarised 

 light will be of use as an additional aid ; wheat-starch 

 presents a faint black cross proceeding from the central 

 hilum, whereas the starch of the oat shows nothing of 

 the kind. 



Fig. 190. Potato Starch-yranules, sold under Ike name of British Arrow-root, 

 used to adulterate flour and bread. (Magnified 240 diameters.) 



The diseases of wheat and corn are readily detected 

 under the microscope ; some of which will be seen to be 

 produced by a parasitic fungus, and by an animalcule re- 

 presented in another place : all are more or less dangerous 

 when mixed with articles of food. 



Adulteration of bread with boiled and maslied potatoes, 

 next to that by alum, is, perhaps, the one which is most 

 commonly resorted to. The great objection to the use of 

 potatoes in bread, is, that they are made to take the place 



