86 MICROSCOPIC OBJECTS. 



granules of starch are either triturated ov immersed in 

 hot water, the skin of the granules will be ruptured. 

 Iodine will then turn them blue, and as microscopic 

 objects they cease to be of value. This circumstance it 

 is very important to remember ; for in testing lichens and 

 other low tribes of plants for starch by iodine, those parts 

 which are inclosed in a membrane are not acted upon, 

 and hence are inferred not to contain starch, while in 

 reality they do contain that aliment. Starch is readily 

 separated from wheat, potato, &c., by washing it in cold 

 water. To obtain this proximate principle from rice, 

 it is necessary to macerate it for a few days ; and to pre- 

 vent the decomposition of the gluten, a little soda should 

 be added to the water. As microscopic objects the 

 various kinds of starch are not only interesting on account 

 of difference of size and form, but also as presenting, 

 with polarized light, the beautiful phenomenon of the 

 black cross. For this purpose it is well to select granules 

 of Tons les mois (Canna coccineaj on account of their large 

 size. 



Under the microscope the surface of the grains often 

 appear corrugated, and each of them has one or two 

 bright spots ; this spot is called the hilum, and is supposed 

 to be the part where the starch adheres to the cell. 



So important an amylaceous alimentary principle of 

 respiration as starch, which enters so largely into the 

 composition of the farinaceous articles of food, deserves 

 to be minutely investigated. 



It will be well for those interested in the purity of these 



