ORGANS AND PROCESSES OF DIGESTION 61 



etc., and prepare them as follows: In the first place 5 c.c. 

 of the glycerine solution or dissolved pepsin and dilute with 

 10 c.c. of water. In the second tube put 15 c.c. of the 

 0.2% hydrochloric acid. In the third, fourth, and fifth tubes 

 place 15 c.c. of glycerine solution which has been diluted 

 previously with ten parts of 0.2% hydrochloric acid to one of 

 glycerine solution. Prepare the sixth tube in the same way 

 as the third and then add 5 c.c. of concentrated hydrochloric 

 acid. Prepare the seventh tube in the same way as the third 

 and then add 5 c.c. of caustic soda solution. Add to each of 

 the seven tubes some minced white of egg, and shake. Place 

 Tubes 1, 2, 3, 6, and 7 in a temperature of 36° C. and keep 

 at this temperature for twenty-four hours. Place Tube 4 in 

 ice. Keep Tube 5 in boihng water. 



At the end of twenty-four hours examine all the tubes. 

 In which is the white of egg dissolved? What nutrient forms 

 the bulk of white of egg? From the result in Tube 2, does 

 hydrochloric acid alone dissolve white of egg? What is the 

 effect of cold on the action? of high temperature? Does ex- 

 cess of hydrochloric acid help or hinder action? Why is a 

 basic substance Hke sodium bicarbonate given in case of sour 

 stomach? Does pepsin act in the presence of a strong base 

 hke caustic soda? (Pepsin requires for its action a sUghtly 

 acid medium, such as is found in the stomach.) Will ptyalin 

 act in an acid medium? Can it convert starch to sugar in 

 the stomach? 



Now place the contents of Tube 3, containing the dis- 

 solved proteid, in the dialyzer, and put distilled water in 

 the outer jar. After twenty-four hours test the water 

 in the outer jar by the xanthoproteic and biuret 

 tests for proteid. Does the proteid solution pass through 

 the membrane? Does white of egg dialyze? (See Ex. 



