54 PHYSIOLOGICAL CHEMISTRY. 



the alimentary canal, and under that form are absorbed into the cir- 

 culation. 



It is evident, therefore, that starch, although the earliest organic mat- 

 ter produced by vegetation, is not the form under which it takes part 

 in nutrition. It is mainly formed in the leaves, but remains there only 

 as a temporary product. Its granules become liquefied, and it is trans- 

 ported, as soluble dextrine or sugar, to other and distant parts of the 

 plant. There it resumes the solid form, and is either changed into cel- 

 lulose, for the woody fibre of the growing tissues, or is deposited as 

 starch in the seeds, tubers, or fleshy roots of the plant. It is in these 

 situations that the principal accumulation of starchy matter takes place ; 

 and it there forms a reserve material, to be afterward employed for the 

 nutrition of animals, or for the growth of the young plant. In either 

 case it again undergoes a preliminary transformation. In the germina- 

 tion of a seed, its starch is liquefied by conversion into dextrine and 

 sugar, before it can be appropriated by the growing tissues ; and if con- 

 sumed as food by man or animals, it undergoes the same transformation 

 in the digestive process. 



Sugar. 



The proximate principles designated under this name include a vari- 

 ety of substances which have certain well-marked characters, and are 

 of frequent occurrence in both animal and vegetable juices. They are 

 crystallizable and soluble in water, and have, when in solution, a sweet 

 taste, which, in some varieties, is very highly developed. They are all 

 decomposed by heating with sulphuric acid ; their hydrogen and oxygen 

 being driven off, while the carbon remains behind as a black deposit. 

 In this condition they are said to be carbonized. The proportions in 

 which they occur in various articles of food, according to the tables of 

 Payen, Yon Bibra, and a few other observers, are as follows : 



QUANTITY OF SUGAR IN 100 PAETS IN 



Cherries . . . 18.12 Wheat flour . . . 2.33 



Apricots . , . 16.48 Rye flour . . - 3.46 



Peaches . . . 11.61 Barley meal . . . 3.04 



Pears .... 11.52 Oatmeal . . . 2.19 



Juices of sugar-cane . 18.00 Indian corn meal . . 3.71 



Sweet potatoes . . 10.20 Cow's milk . . 5.20 



Beet roots . . . 8.00 Goat's milk . . . 5.80 



Parsnips . . . 4.50 Beefs liver . . .1.79 



The most important varieties of this substance, in a physiological 

 point of view, are glucose, cane sugar, and milk sugar. 



1. Glucose, C 6 H 12 6 . 



Glucose, also called grape sugar, from its abundance in the juice of 

 the ripe grape, may be considered as the representative of the saccha- 

 rine substances. It occurs more frequently than any other in the ani- 

 mal fluids, being found in the juices of the liver, in the chyle, the blood, 

 and the lymph. In diabetes it is abundantly excreted with the urine. 



