DIGESTION AND ABSORPTION ] 57 



ether, chloroform, calcium chloride, 25 per cent, solution NaOH, 

 25 per cent, solution KOH, and one-half saturated solution Na 2 CO 3 . 

 Non-medicated absorbent cotton for rapid filtering of mucilaginous 

 or k albuminous liquids. 



I. THE CARBOHYDRATES. 







1. Materials. Potato starch, dextrin, dextrose, maltose, lactose, 

 saccharose, and cellulose, represented by absorbent cotton and 

 ashless filter paper. 



2. Preparation. (1) To prepare Fehling's Solution, (a) Into a half- 

 litre, glass-stoppered bottle put 34.64 grams CuSO 4 , c. p., and enough 

 H 2 O dist. to make 500 c.c. Label the solution: Fehling's Solution (a). 



(b) Into a similar receptacle put 173 grams of potassic-sodic tartrate, 

 KNaC 4 H 4 O + 4H 2 O (Rochelle salt), and 50 grams of NaHO, weighed 

 in sticks; add enough water to make 500 c.c. Label: Fehling's 

 Solution (b). For use, mix these solutions in equal parts. A con- 

 venient quantity for the following experiments is 100 c.c. of each 

 solution. 



(2) Prepare a starch paste by rubbing 1 gram of starch to a creamy 

 consistence with water, add 100 c.c. of distilled water, and f boil. 



(3) Prepare a dilute solution of iodine by direqt solution in water 

 or by diluting an alcoholic solution. 



3. Experiments and Observations. (1) Put a little dry starch 

 into an evaporating dish; add some dilute iodine. The starch turns 

 blue. Pour a few drops of starch paste into a test-tube; 'add a few 

 drops of iodine. Iodine may be used to detect the presence of raw 

 or of cooked starch. 



(2) Put some raw starch into a test-tube or beaker; add water and 

 stir. The starch does not seem to be at all soluble in water. Stir 

 or shake the mixture to bring the starch into suspension in the water; 

 pour upon a filter. X clear filtrate passes readily through. Test 

 the filtrate for starch; result, negative; pour a few drops of iodine 

 upon the filter, starch present. Conclusions: 



(a) Potato starch is insoluble in cold water. 

 (6) The granules of potato starch will not pass through common 

 filter paper. 



(3) Dilute a few centimetres of starch paste; pour it upon a filter; 

 to the filtrate add iodine. The blue color indicates that in the cook- 

 ing of starch the grains are broken up into particles sufficiently 

 small to pass readily through the meshes of common filter paper. 



(4) In order to determine whether dilute starch paste will, in 

 response to the laws of osmosis, pass through an animal membrane, 

 fill a dialyzer with dilute starch paste. Set aside to be tested one 

 or two days later. 



