298 



VITANTITATIVE ESTIMATION OF SUGAR. 



150. Quantitative Estimation of Sugar. 



I. By Fermentation. Into the glass vessel 



^_ ^- (Fig- 121, ) a measured quantity (20 cmtr.)of 



the fluid (sugar) is placed along with some yeast, 

 while b contains concentrated sulphuric acid. 

 The whole apparatus is now weighed. When 

 exposed to a sufficient temperature (10-40C.), 

 the sugar splits into 2 molecules of alcohol and 

 2 of carbonic acid, 



MM* 



Fig. 121. 



Apparatus for the quantitative 

 estimation of sugar by fer- 

 mentation. 



C 6 H 12 6 = 2 (C 2 H 6 0) +2 (C0 a ), 

 Grape-sugar = 2 alcohol + 2 carbonic acid ; 



and in addition there are formed traces 

 of glycerine and succinic acid. The COg 

 escapes from b, and as it passes through the 



H 2 S0 4 , C0 2 yields to the latter its water. The apparatus is weighed after two 

 days, when the reaction is ended, and the amoiiut of sugar is calculated from the 

 loss of weight in the 20 cmtr. of fluid. 100 parts of water-free sugar = 48 "89 

 parts COg, or 100 parts C0 2 correspond to 204'54 parts of sugar. 



II. Titration. By means of Fehling's solution, which consists of cupric sul- 

 phate, tartrate of potash and soda, caustic soda, and water. It is made of such 

 a strength that all the copper in 10 cubic centimetres of the solution is reduced by 

 0'05 grammes of grape-sugar (see Urine, vol. ii.). 



III. The amount may also be estimated by the polarisation apparatus (see Urine, 

 vol. ii.). 



151. Mechanism of the Digestive Apparatus. 



This embraces the following acts : 



1. The introduction of the food; the movements of mastication and 

 those of the tongue ; insalivation and the formation of the bolus of food. 



2. Deglutition. 



3. The movements of the stomach, of the small and large intestine. 



4. The excretion of faecal matters. 



152. Introduction of the Food. 



Fluids are taken into the mouth in three ways: (1) By suction, the lips 

 are applied air-tight to the vessel containing the fluid, while the tongue is 

 retracted (the lower jaw being often depressed) and acts like the piston in 

 a suction pump, thus causing the fluid to enter the mouth. Herz 

 found that the negative pressure caused by an infant while sucking 

 = 3-10 mm. Hg. (2) The fluid is Japped when it is brought into 

 direct contact with the lips, and is raised by aspiration and mixed 

 with air so as to produce a characteristic sound in the mouth. (3) 

 Fluid may be poured into the mouth, and as a general rule the lips are 

 applied closely to the vessel containing the fluid. 



The solids when they consist of small particles are licked up with 

 the lips, aided by the movements of the tongue. In the case of large 



