252 UNCONSCIOUS NERVOUS OPERATIONS 



be sure that the sugar is a product of digestion, Trommer's test 

 should be applied to the solution before saliva is added, and also to 

 dilute saliva. 



Prepare two other test tubes in a similar way, but boil the contents 

 of one, and place the other on ice, or in a very cool place. From this 

 conclusions may be drawn regarding the relation of temperature to 

 the activity of the ferment of saliva. 



The saliva of some persons has little or no digestive effect, hence 

 this experiment will occasionally fail. 



114. Gastric Digestion. Fill three test tubes about half full of 

 artificial gastric juice, 1 and three other test tubes with (1) water, (2) 

 water containing a little powdered pepsin, and (3) a ^ per cent 

 muriatic acid solution, respectively. Place in each test tube a few 

 shreds of fibrin. Fibrin is used because it is a solid proteid, and 

 the progress of its digestion can be followed with the eye, without 

 making special tests. Boiled white of egg may be used, but it 

 digests more slowly. Boil one test tube containing artificial gastric 

 juice, place a second on ice, and set away the other test tubes in a 

 warm (37 C.) place. 



In a short time the fibrin in the tube of gastric juice kept in the 

 warm place is seen to be much swollen, and gradually it disappears 

 iii solution. Compare the test tube with the others. What effect 

 has temperature on gastric digestion? Is the presence of pepsin 

 necessary? \Does pepsin alone (in water) digest the fibrin? 



115. Action of Gastric Juice on Milk. To a test tube about half 

 full of fresh milk, add a little artificial gastric juice that has been 

 neutralized by the addition of dilute carbonate of soda. Keep at a 

 temperature of about 37 C. (98 F.). In a short time the milk 

 curdles. In previous experiments on milk, curdling was produced 

 by acids; here, since the gastric juice was neutralized, it is due to 

 some other cause. To the test tube add a little dilute muriatic acid to 

 acidulate the contents, and keep it in the warm place for several hours. 

 The casein is finally digested in the presence of acid, forming a straw- 

 colored fluid. 



116. Action of Rennet on Milk. To some fresh milk en a test 

 tube add a little commercial extract of rennet, and keep at a tempera- 



1 Add a little powdered pepsin (to be obtained at a druggist's) to a 

 ^ a per cent solution of muriatic (hydrochloric) acid. 



