CHAPTER XLII. 

 ENZYMES AND DIGESTION. BUFFERS. 



IV. Enzymes and Digestion. 



1. Ptyalin from saliva, (a) Test a biscuit for sugar with 

 Fehling's solution. Chew a biscuit until it tastes sweet. Now test 

 with Fehling's. Explain result, (b) Collect a few c.c. of saliva 

 in a beaker (the flow of secretion may be accelerated by chewing 

 paraffin) ; dilute the saliva with about 5 vols. H 2 O. Make the 

 following mixtures: (1) equal vols. starch paste and saliva, (2) the 

 same, except using saliva that has been previously boiled, (3) same 

 as (1) +5 drops 10% HC1, (4) same as (1) +5 drops 10% KOH. 

 Divide (1) into two portions and set one outside window. Warm 

 all the other mixtures to 37-40 C. (not higher) and maintain at 

 40 C. for 10 minutes. Test each mixture for starch (using iodine) 

 and for sugar (Fehling's). Discuss your results. 



2. Pepsin. Prepare 12 Mett's Tubes of egg-white in the manner 

 demonstrated. Prepare test-tubes containing: (a) 1% pepsin in 

 1% Na 2 CO 3 . (b) 1% pepsin in 0.03 N HCL. (c) 1% pepsin in/ 

 H 2 O. To each of these add a Mett's Tube and try effect on each ^ 

 combination of (a) cold (out of window), (b) room temperature,^ 



(c) 40 C. (d) 100 C. for 10 minutes then 40 C. Make quanti- T! 

 tative estimations at different time intervals. Results. 



3. Coagulating Enzymes. Rennin. Prepare (a) 5 c.c. fresh milk */ 

 + 0.03 N HCL until a ppt. formed, (b) 5 c.c. fresh milk+5 drops fi< 

 rennin. (c) 5 c.c. fresh milk+5 drops rennin + 5 drops 1% Na 2 CO 3 . >^e 



(d) 5 c.c. fresh milk+5 drops 0.03 N HCL. Let stand for one hour A 

 and compare: (a) is for control to compare with (d)., Try (a) after 

 boiling rennin. 



4. Oxidizing Enzymes. Add H 2 O 2 to blood. Is the presence 

 of catalase shown? Try bits of spleen, liver, lung, kidney and 

 muscle of frog. Which gives greatest catalytic action? Boil each 

 of these tissues and repeat. Add solution of guiacum to a slice of 

 potato. Blue colour indicates "active" oxygen. In what part 



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