ADULTERATION OF FOOD. 



347 



by which the loaf is made to weigh heavier. By dissolving 

 out the alum in water and then re-crystallising it under 

 the microscope, this adulteration is readily detected. 



Before leaving the subject of starch, allusion may be 

 made to the prevalent and destructive epidemic amongst 

 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, fig. 188. Hence it may be 



Fig. 182. — Structure and Character of genuine Ground Coffee. {After Hassall.) 



inferred, that the natural nutriment of the plant being 

 deficient, the haulm dies, the cells of the tuber soon turn 

 black and decompose ; and fungi developed as in most 

 other decaying vegetable substances. 



" This will undoubtedly explain the most prominent 

 symptom of the potato-disease, the tendency to decom- 

 position ; and is a point in which the microscope confirms 

 the result of chemical experiment : for it has been found 



