THE CARBOHYDRATES. 11 



LESSON II. 

 THE CARBOHYDRATES, FATS, BONE. 



1. I. Starch (0 6 H 10 O 5 ) M Preparation. Wash a potato 

 thoroughly, and grate it on a grater into water in a tall 

 cylindrical glass. Allow the suspended particles to subside, 

 and after a time note the deposit ; the lowest stratum consists 

 of a white powder or starch, and above it lie coarser fragments 

 of cellulose and other matters. Decant off the supernatant 

 fluid. 



(a.) Microscopical Examination. Examine the white de- 

 posit of starch, noting that each starch granule shows an 

 eccentric hilum with concentric markings. Add a very 

 dilute solution of iodine. Each granule becomes blue, while 

 the concentric markings become more distinct. 



(b.) At this stage it is advantageous to compare the 

 microscopic characters of other varieties of starch e.g., rice, 

 arrowroot, &c. (Fig. 1). 



Fig. 1. e, Tahiti arrowroot ; d, Potato starch. 



(c.) Polariscope. Examine starch granules with a polari- 

 sation-microscope. With crossed Nicol's, when the field is 

 dark, each granule shows a dark cross on a white refractive 

 ground. 



(d.) Squeeze some dry starch powder between the thumb 

 and forefinger, and note the peculiar crepitation sound and 

 feeling. 



