1210 STARCH. 



nucleo-proteid yield additionally some form of carbohydrate by hydro- 

 lytic cleavage. To these the name of nucleo-glycoproteid may per- 

 haps be conveniently applied. They have been so far described as 

 obtained from the pancreas and mammary gland. 



CARBOHYDRATES. 



Certain members only of this extensive class have been 

 found in the human body ; of these, the most important and 

 wide-spread are glycogen, grape-sugar or dextrose (glucose), 

 with which diabetic sugar seems to be identical, maltose and 

 milk-sugar. 



Although the above-mentioned carbohydrates may be de- 

 tected in various tissues and secretions of the animal body, 

 their presence in the several cases is not so much due to their 

 introduction into the body in the form in which they there 

 occur as to their production from other members of the car- 

 bohydrate group existing in food. The chief of these is starch, 

 and it will perhaps conduce to completeness to deal first very 

 briefly with this parent-substance and some of the products of 

 its decomposition. 



The Starch Group. 

 1. Starch (C 6 H 10 O 5 ) n . 



Starch occurs characteristically in plants and is formed in 

 their green parts under the determinant influence of the chloro- 

 phyll-corpuscles. The exact mode of its formation is how- 

 ever as yet undecided. It exists in plant-tissues in the form 

 of grains which vary in size and shape according to the plant, 

 but which possess the common characteristic of exhibiting a 

 stratified structure, which is much more marked in some cases 

 (potato-starch) than in others, and the phenomena of double- 

 refraction when examined in polarized light. Considered as a 

 whole the grains appear to be composed of two substances, of 

 which the chief both in quantity and importance is called gran- 

 ulose and the other cellulose. The former, which yields the 

 blue colour characteristic of starch on the addition of iodine, 

 may be dissolved out by the action of saliva or malt-extract, 

 leaving a cellulosic skeleton of the original grain. This 

 so-called cellulose is not identical with ordinary cellulose, as 

 shewn by its ready solubility in several reagents which do not 

 dissolve the latter. When treated with boiling water the grains 

 swell up and finally burst, yielding a uniform viscous mass of 

 starch-paste of which the chief component' is the granulose. 

 The mass thus obtained cannot be regarded as a true solution 

 of starch, and it filters with extraordinary difficulty, leaving 



