224 DIGESTION AND ABSORPTION 



Conclusion. — 1. Write a paragraph telling the uses and struc- 

 ture of a gland. 



2. Make a diagram showing the parts of a gland. 



Proble^n 187 : To find the use of digestion. 



Materials. — Starch paste, saliva, thistle tubes with membrane 

 covers, Fehling's solution, lamp, battery jar containing warm 

 water (about 100° F.). 



Method. — In one thistle tube place some saliva mixed with 

 starch paste. In a second tube place some paste and water. 

 Fasten membrane covers over the thistle tubes, and wash carefully 

 to rid of all starch or other material on outside of tube. Then 

 place the two thistle tubes, large end down, in the jar containing 

 warm water. Next test some saliva with Fehling's solution. 

 Is there any grape sugar present? At the end of the laboratory 

 period test the contents of the jar with iodine and with Fehling's 

 solution. Was there any starch in the water? Grape sugar? 



Conclusion. — 1. What caused the presence of this grape sugar 

 in the jar? 



2. How did it get into the jar? 



Prohle^n 188 : To determine the conditions most favorable 

 for gastric digestion. 



Materials. — Test tubes, eggs, hydrochloric acid, pepsin, caustic 

 soda, copper sulphate. 



Method. — Use five test tubes or beakers and some boiled white 

 of egg. In No. 1, place minced white of egg and water ; in No. 2, 

 place minced white of egg and .2 per cent hydrochloric acid ; 

 in Nos. 3, 4, and 5, place minced white of egg, .2 per cent hydro- 

 chloric acid and pepsin. 



Keep the first three in a warm place at about a temperature of 

 blood heat for several hours. Keep No. 4 in an ice box or sur- 

 rounded by cracked ice. Keep No. 5 in boiling water for 15 or 

 20 minutes, then place it in the warm place with Nos. 1, 2, and 3. 



Observations. — Test No. 1 with biuret test ^ for the presence of 



1 Biuret solution : To the material to be tested add its own bulk of concen- 

 trated caustic soda. Then add a drop or two of weak copper sulphate solution. 

 A violet or blue color shows the presence of unchanged protein, a rose pink the 

 presence of peptone. 



