102 PUBLIC HEALTH CHEMISTRY 



powder to the water-drop, and mix. Put on a cover-glass, 

 remove excess of water, and examine with a microscope, 

 using first a f inch objective and then a inch. Observe 

 carefully the following points : (i) Shape ; (2) Size ; (3) 

 Hilum (presence or absence of) ; (4) Slriations (presence or 

 absence of). Iodine solution sho\vs up the striae, (i-iooo). 

 Starches fall into five groups : 



1. Contour round the wheat group wheat, barley, 

 and rye. These all have grains large and minute (rye has 

 also intermediary sizes, as also has barley to a less 

 extent), and have no very apparent hilum or striae. 



2. Contour oval pea, bean, and lentil. These all have 

 grains of large size with a longitudinal hilum, with very 

 faint striae. 



3. Contour ovoid potato and arrowroot. Large granules, 

 with a distinct hilum and well-marked concentric rings or 

 striae. The hilum is at the smaller end (oyster shape) in 

 potato, and at the other end in arrowroot, the granules of 

 which are smaller (except tous-les-mois variety). 



4. Contour semi-faceted sago and tapioca. These have 

 a hilum and ill-defined rings. The sago grains are the larger. 



5. Contour faceted maize, oats, and rice. The rice 

 granules are the smallest, the maize the largest, and they 

 have a stellate hilum. 



The polariscope gives valuable aid in differentiation. 



CARBOHYDRATES. 



Carbohydrates are compounds of carbon, hydrogen, and 

 oxygen, the two latter being present in the same proportion 

 in. which they combine to form water. The class is a large 

 one, and its components are widely distributed in Nature. 

 The carbohydrates may be arranged into three groups, viz. : 



1. Monosaccharids or Glucoses, including dextrose (or 

 grape sugar), laevulose (or fruit sugar), and galactose. 



2. Disaccharids or Sugars, including saccharose (sucrose 

 or cane sugar), lactose (or milk sugar), and maltose (or malt 

 sugar). 



3. Polysaccharids or Starches, including starch, dex- 

 trin, gum and cellulose, inulin, and glycogen. 



From allied groups certain substances used in bac- 

 teriology are derived, and are enumerated here for the 



