POLYSACCHARIDS OR AMYLOSE8. 95 



to which acetic acid has been added, is reduced by dextrose, but 

 not by maltose. 



Isomaltose. When starch is acted on by any of the enzymes 

 which produce maltose isomaltose is also formed ; unlike maltose, 

 it is not directly fermentable by yeast. It is very soluble in water, 

 and is sweet in taste. It occurs in small quantity in the urine. 



Polysaccharids or Amyloses. The formula of this group 



is (C 6 H 10 5 V 



The exact formula is not determined. Chemists agree that it 

 is not C 6 H 10 O 5 , but some multiple of this, as indicated by " n," and 

 that u n" is not less than five. The members of the group are : 

 Starch, Amylodextrin, Erythrodextrin, Achroodextrin, Maltodex- 

 trin, Glycogen, and Cellulose. 



Starch. Starch is not found in the human body except when 

 it is taken in as food. It is -very abundant in vegetable food. In- 

 deed, it is said that starch exists in every chlorophyll-containing 

 plant at some period of its existence. Starch is a substance of 

 great interest, from the fact that it is the first organic substance 

 produced by vegetables from inorganic matter. Animals have 

 not the power to produce organic substances directly from mem- 

 bers of the inorganic kingdom, but plants have this power, and 

 they exercise it, and from the organic materials thus produced 

 animals are nourished. Animals may change the organic matter 

 from one form to another, as starch to sugar, but were inorganic 

 substances alone supplied to animals they would starve. 



The inorganic substances out of which the plant forms the 

 starch are carbonic acid and water, these being taken from the 

 atmosphere and the soil. This process is represented by the fol- 

 lowing formula : 



(6C0 2 + 5H 2 0) n = (C 6 H 10 5 ) n + O n 



Carbonic acid. Water. Starch. Oxygen. 



That is, the carbonic acid and the water are decomposed, the car- 

 bon and hydrogen, with some of the oxygen, unite and form 

 starch, while the rest of the oxygen is set free. To bring about 

 this change there must be present solar light and the green color- 

 ing-matter, chlorophyll. If chlorophyll is absent, this change 

 does not take place, nor does it when solar light is absent. 



Starch exists in plants in the form of grains, known as 

 " starch-grains" or " starch-granules" (Fig. 83). They present a 

 characteristic appearance under the microscope by which they 

 may at once be recognized. Each granule presents a number 

 of concentric markings and varies in size and shape in different 

 plants; by these points of difference the plant from which the 

 granules are derived may be identified. This fact is made use of 

 in detecting adulterations, in which cheaper kinds of starch are 

 mixed with more expensive kinds and sold for the latter at a 



