CARBOHYDRATES AND RELATED BODIES. 4! 



in which / expresses the length of the observation tube in millimeters and 

 c the concentration or strength of the solution in grams per 100 cubic 

 centimeters. 



For many substances this rotation is so characteristic and so easily ob- 

 served that it constitutes a good test of purity ^ or identity. With the 

 specific rotation known the following relation enables us to find the amount 

 of active substance in solution : 



The following are some specific rotations which have importance from the 

 standpoint of physiological chemistry, the temperature being 20 C. in each 



case : 



Cane sugar, [a]/> + 66.5 for c=io to 30 



Milk sugar (+H 2 O), [<L]D = + 52.5 c 3 to 40 



Malt sugar (+H 2 O), [a]x> = + I37-O c= 2 to 20 



Glucose, [a] D = + 53.0 c = 20 



Levulose, [a] /> = 93.0 c = 10 to 20 



Invert sugar, [a] D = 20.2 c=i5 



The protein substances, dextrin, glycogen and a number of other com- 

 pounds to be referred to later have also a high rotating power, which 

 finds application in investigations. 



THE POLYSACCHARIDES. 



We have here a very important group of bodies, some of 

 which appear to have an extremely complex structure. For- 

 merly these compounds were assumed to be simpler than the 

 sugars and were represented by the general formula C 6 H 10 O 5 . 

 The action of water in producing glucose was assumed to con- 

 sist merely in the addition of one molecule as shown by the 



formula : 



C fl H 10 5 + H 2 = C 8 H 12 6 . 



But this view is no longer held ; the starches, cellulose bodies 

 and certain gums belonging to the group have been shown to 

 exist in the form of large and probably very complex mole- 

 cular aggregations, and the formula (C 6 H 10 O 5 ) n is now 

 usually employed to indicate this fact. 



These polysaccharides are related to the real sugars by sev- 

 eral reactions. By certain treatment most of them may be 

 converted more or less readily into maltose, glucose or fruc- 



