NON-NITROGENIZED ALIMENTARY SUBSTANCES. 171 



used as food. The sugars derived from the vegetable kingdom are cane- 

 sugar, under which head may be classed all varieties of sugar except that ob- 

 tained from fruits, and grape-sugar, which comprises all the varieties existing 

 in fruits. The following are the formulae for the different varieties of sugar 

 in a crystalline formj 



Cane-Sugar (Saccharose), C^H^On 



Milk-Sugar (Lactose), C^H^Ojg 



Grape-Sugar (Glucose, Dextrose), C 6 H 12 6 



All varieties of sugar have a peculiar, sweet taste ; they are all soluble in 

 water, glucose being more soluble than cane-sugar or lactose; glucose is 

 sparingly soluble in alcohol, which dissolves small quantities, only, of cane- 

 sugar or lactose ; glucose ferments readily and is changed into alcohol and 

 carbon dioxide ; cane-sugar and lactose are said to be incapable of fermenta- 

 tion, but cane-sugar may easily be converted into fermentable glucose, and 

 lactose, into a fermentable sugar called galactose, by boiling with dilute 

 mineral acids ; they are capable of being converted into lactic acid in the 

 presence of decomposing nitrogenized matters ; they are inflammable, leav- 

 ing an abundant carbonaceous residue and giving off a peculiar odor of cara- 

 mel ; they undergo other modifications when treated with the mineral acids 

 or with alkalies, which are interesting more in a chemical than a physiolog- 

 ical point of view. Of all the varieties of sugar, that made from the sugar- 

 cane is the most soluble, the sweetest and the most agreeable. Beet-root 

 sugar is identical with cane-sugar. 



Much of the sugar used in the nutrition of the organism is formed in the 

 body by the digestion of starch. This transformation of starch may be 

 effected artificially. The sugar thus formed, called glucose, is identical in 

 composition with grape-sugar. Except in the milk during lactation, this 

 is the only form in which sugar exists in the organism, all the sugar of the 

 food being converted into glucose before it is taken into the blood. 



Starch. A non-nitrogenized substance, closely resembling sugar in its 

 ultimate composition (C 6 H 10 5 ), is contained in abundance in a great num- 

 bor of vegetables. It is found particularly in the cereals (wheat, rye, corn, 

 barley, rice and oats), in the potato, chestnuts, and in the grains of legumi- 

 nous plants (beans, peas, lentils and kidney-beans), in the tuberous roots of 

 the yam, tapioca and sweet-potato, in the roots of the maranta arundinacea 

 (arrowroot), in the sago-plant and in the bulbs of orchis. In the cereals, 

 after desiccation, the proportion of starch is usually between sixty and sev- 

 enty per cent. It is most abundant in rice, which contains, after desiccation, 

 88-65 per cent. 



When extracted in a pure state, starch is in the form of granules, varying 

 in size between Io ^ 00 and -yfa of an inch (2'5 and 62*5 //,), and presenting, in 

 most varieties, certain peculiarities of form. The granule frequently is 

 marked by a little conical excavation called the hilum, and the starch- 

 substance is arranged in the form of concentric laminaa, the outlines of 

 which are often quite distinct. When starch is rubbed between the 

 fingers, these little, hard bodies give it rather a gritty feel and produce a 



