42 G THE MICROSCOPE. 



from that of another. In some cases the microscopic examination is 

 aided by an application of the solution of potash. Thus we may 

 readily detect the mixture of wheat-flower with either potato-starch, 

 meal of the pea, and bean, by the addition of a little water to a 

 small quantity of the flour ; then, by adding a few drops of a solution 

 of potash (made of the strength one part liquid potash to three parts 

 of water), the granules of the potato-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 ren- 

 dered very obvious under the microscope. Polarised light may be used 

 as an additional aid in this detection ; wheat-starch presents a beau- 

 tiful black cross proceeding from the central hilum, whereas the starch 

 of the oat shows nothing of the kind. 



The diseases of wheat and corn are most readily detected under the 

 microscope ; these will be seen to be produced by a parasitic fungus, as 

 well as the animalcule represented in a previous chapter : all of which 

 are more or less dangerous if used as articles of food when in this state. 



Adulteration of bread with boiled and masJied 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 of an article very much more nutritious. 



This adulteration may be readily detected by means of the micro- 

 scope. The cells which contain the starch-corpuscles are in the potato 

 very large, fig. 205 ; in the raw potato they are adherent to each 

 other, and form a reticulated structure, in the meshes of which the well- 

 defined starch-granules are clearly seen ; in the boiled potato, however, 

 the cells separate readily from each other, each forming a distinct 

 article : the starch-corpuscles are much less distinct and much altered in 

 their form. 



Adulteration with alum and " stuff ? This adulteration is prac- 

 tised with a twofold object : first to render flour of a bad colour and 

 inferior quality white and equal, in appearance only, to flour of supe- 

 rior quality ; and secondly, to enable the flour to retain a larger propor- 

 tion of water, by which the loaf is made to weigh heavier. 



Before leaving the subject of starch, allusion may be made to the 

 prevalent and destructive epidemic among potatoes, which is a disease 

 of the tuber, not of the haulm or leaves. 



" Examined in an early stage, such potatoes are found to be composed 

 of cells of the usual size ; but they contain little or no starch : this will 

 be seen upon reference to Nos. 16 and 17, Plate XVI. Hence it may 



