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. 192. — 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 wdiich the microscope confirms 

 the result of chemical experiment : for it has been found 



