12 PHYSIOLOGICAL CHEMISTRY. 



acetone, stir and after permitting the acetone mixture to stand for 

 a few minutes filter on a Buchner funnel. The resulting precipi- 

 tate, after drying and pulverizing, may be used to demonstrate 

 vegetable sucrase. 



4. Demonstration of Vegetable Sucrase. To about 5 c.c. of a 

 one per cent solution of sucrose in a test-tube add a small amount 

 of the sucrase powder prepared as directed above. Place the tube 

 at 38 C. for 24-72 hours and at the end of that period test the 

 solution by Fehling's test. Reduction indicates that the active 

 sucrase powder has transformed the non-reducing sucrose into 

 dextrose and Isevulose, and these sugars, in turn, have reduced the 

 Fehling solution. 



5. Preparation of an Extract of Lactase. 1 Treat the finely 

 divided epithelium of the small intestine of a kitten, puppy, or pig 

 embryo with about three volumes of a two per cent solution of 

 sodium fluoride and permit the mixture to stand at room tempera- 

 ture for twenty- four hours. Strain the extract through cloth or 

 absorbent cotton and use the strained material in the following 

 demonstration. 



6. Demonstration of Lactase. 2 To about 5 c.c. of a one per 

 cent solution of lactose in a test-tube add about one cubic centi- 

 meter of a toluene-water extract or a two per cent sodium fluoride 

 extract of the first part of the small intestine 3 of a kitten, puppy, or 

 pig embryo prepared as described above. Prepare a control tube 

 in which the intestinal extract is boiled before being added to the 

 sugar solution. Place the two tubes at 38 C. for 24 hours. At 

 the end of this period add one cubic centimeter of the digestion 

 mixture to 5 c.c. of Barfoed's 4 reagent and place the tubes in a 

 boiling water-bath. 5 Examine the tubes at the end of three min- 

 utes against a black background in a good light. If no cuprous 

 oxide is visible replace the tubes and repeat the examination at the 

 end of the fourth and fifth minutes. If no reduction is then ob- 

 served permit the tubes to stand at room temperature for 5-10 min- 

 utes and examine again. 6 



1 For a discussion of this enzyme see p. 144. 

 3 Roaf; Bio-Chemical Journal, 1908, III, p. 182. 



3 Duodenum and first part of jejunum. 



4 To 4.5 grams of neutral crystallized cupric acetate in 900 c.c. of water, add 

 0.6 c.c. of glacial acetic acid and make the total volume of the solution one liter. 



5 Care should be taken to see that the water in the bath reaches at least to the 

 upper level of the contents of the tubes. 



8 Sometimes the drawing of conclusions is facilitated by pouring the mixture 

 from the tube and examining the bottom of the tube for adherent cuprous oxide. 



