DIGESTION AND ABSORPTION 161 



(a) To a portion of saliva add an equal volume of 0.3 per cent, 

 hydrochloric acid and the same amount of starch paste. The mix- 

 ture represents 0.1 per cent, hydrochloric acid. Place the mixture 

 in the incubator for fifteen minutes; test with Fehling's solution. 

 Verdict? 



(b) Repeat the experiment, substituting for the hydrochloric acid 

 lactic acid of the same strength; place in the incubator for fifteen 

 minutes; test with Fehling's solution. 



What is the conclusion? 



(12) To Determine the Course of Salivary Digestion. Mix 50 c.c. 

 of salivary extract with an equal amount of starch paste. Test a 

 portion with iodine at once. Test another portion at once with 

 Fehling's solution. Keep the beaker in a water-bath at blood temper- 

 ature. Test a portion of the mixture every minute with iodine and 

 another portion every minute with Fehling's solution. 



(a) What is the first change noted in the digestion of the starch ? 

 (6) How many steps may be made out with the means used and 

 under the conditions existing in the experiment? 



(c) In what order do the changes occur? 



(13) Place some starch paste in a beaker which may be floated 

 in ice-water; similarly float a beaker with saliva. After both liquids 

 have been cooled down to near the temperature of the surrounding 

 water, mix them in one of the beakers, keep the mixture at the 

 low temperature while subjecting portions of it every two minutes 

 to the tests suggested above. 



(a) May the same changes be made out in this experiment as in 

 the previous one? 



(b) Are the changes in the same order? 



(c) State any differences in salivary digestion at blood temperature 

 and at low temperature (0 C.) used in this experiment. 



(14) (a) Sum up the day's work in a series of conclusions. 



(b) What is the chemical formula of starch? Of erythrodextrine ? 

 Of maltose? Of dextrose? 



(c) Write a chemical reaction or a series of reactions which will 

 be in harmony with the observations and show as nearly as possible 

 the course of salivary digestion. 



(d) What change has the ferment wrought in the starch molecule 

 to render the resulting carbohydrate capable of diffusion through 

 animal membrane? 



III. THE PROTEIDS. 



1. Materials. An egg; fibrin; gelatin; myosin; syntonin; acid 

 albumin; commercial peptone (mixed albumoses, proteoses, and 

 peptones); Grubler's pure peptone. 



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